Fermentation.

A Lecture, Delivered by William Johnson,

President of the Pharmaceutical Society of Victoria,

On 5th October, 1871.

It has been observed from time immemorial that certain bodies of a compound character—such as the juice of the grape, also grain flour—were, under certain circumstances, susceptible of a peculiar chemical change in their constitution, by which their general character became more or less altered. Nothing beyond the mere fact was, however, known to the ancients, or indeed moderns until a comparatively very recent date; no explanation offered, no cause assigned for the phenomena.

We read in "sacred writ" that our common ancestor, Noah, planted a vineyard, and, drinking of the wine, was made drunk. Evidently therefore the art of wine-making was known in the time of Noah, and as he is said to have planted a vineyard, he must have derived his knowledge and experience from a period still more remote: therefore the process must have been well known to the ancestors of Noah, even, perhaps, almost up to Adam. Fermentation, therefore, appears to have been one of the first chemical processes known to man. That its useful application to bread-making was known at a very remote period is also certain, for we are informed in Genesis that the Israelites practised the process when they were in bondage in Egypt, for it was during that time the feast of unleavened bread was ordained.

In wine-making all that is requisite is to place the juice of the grape into suitable vessels for a sufficient length of time and in a proper place, when fermentation sets in page 46 spontaneously, and continues to the end of the process. In bread-making and brewing it is necessary to add yeast, a substance composed of gluten, one of the constituents of grain in a certain state of decay or putrefaction, and abounding in a species of fungous growth of a very low type. By many this fungus is believed to be the direct cause of the fermentation; by others, however, this view of the case is much questioned, the cause being rather assigned to contact with a decomposing body. Possibly the truth may lie between these hypotheses; and, whilst allowing with Liebig and his followers that fermentation is excited by contact with a decaying nitrogenous body such as yeast, yet the cause of that decay itself may be, and most probably is due to the attacks of fungi upon it. Without fungi, then, there would be no decomposing gluten, and without decomposing gluten no fermentation.

You are, probably, most of you acquainted with the processes of bread-making and brewing. The latter has been recently ably elucidated in this Lecture Hall, by my friend Mr. Foord, and will therefore be only slightly alluded to by me, and even the process of bread-making need not detain us long. Most of you are doubtless aware that the baker takes Hour, which he mixes up with more or less water, adding a certain proportion of brewers' yeast and salt; and when fermentation has fairly commenced, known by the rising and swelling of the mixture, the whole is well kneaded together; and after a while, when sufficiently risen and strong, the mass is cut up into suitable-sized portions, and placed in the oven to be baked into loaves. During the brief interval of time that has been consumed in the fermentation of the dough, some very intricate changes have ensued.

The causes of these variable proportions being referable to different varieties and to climate.

After the fermentation has proceeded some time, if the dough be examined it will be found to have suffered a loss page 47 of sweetness, arising from the destruction of the sugar contained in the original flour.

There are other sugars, samples of some of which may be found upon the table, including "milk sugar," the peculiar sweetening principle of milk; "manna," a peculiar sugar entirely distinct from ordinary sugar, and said to be not liable to fermentation; and eucalyptus sugar, found under some of our native gum-trees; also glycerrizine, the sweetening principle of licorice.

With most of these, however, we have at present nothing to do; our inquiries will be confined to the two first.

If cane sugar be required to be fermented, it must first be converted into grape sugar; this, as I have already explained, is easily accomplished by appropriating to itself the elements of one atom of water, as in the diagram, a step page 48 which it performs for itself, under the influence of the fermenting principle—viz., yeast. The process now goes on, and the following changes take place in the sugar:—

It will thus be seen that in manufacturing alcohol from ordinary sugar the weight of the product is about half that of the sugar employed, or about the same weight of proof spirit, about one-half of which is water.

In the ordinary process of bread-making precisely similar effects result from the action of the yeast; the sugar contained in the flour is converted into alcohol and carbonic acid, both of which become expelled during the process of baking, thus assisting the bread to rise and acquire that light, spongy appearance so much esteemed in good bread.

A good many years ago a company was started in London for the purpose of collecting and utilising the alcohol eliminated from baking bread, condensers being used for the purpose; but rival bakers, taking the alarm at the threatened injury to their businesses, diligently denounced the whole scheme, representing to their customers that such baked bread must be inferior to the ordinary kind, by virtue of having had all the "'whiskey' taken out of it!" and so successful were they that they eventually succeeded in stifling the novel enterprise. Since that time, I believe, no further attempts have been made to utilise the alcohol so formed, but it has been suffered to go to waste with the escaping carbonic acid.

In referring again to the list of products of the fermentation of sugar in the diagram, it will be observed that there has been no loss of material, the total amount of carbonic acid and alcohol produced equalling the weight of the sugar employed, and the question naturally suggests itself as to how the yeast acts so as to bring about the decomposition of the sugar; had any of the elements of the sugar been abstracted the process would be more intelligible. At present I am unable to give any precise explanation; the two bodies seem, as it were, not in any way to exchange particles. The sugar gives nothing to, and receives nothing from the yeast; yet by some peculiar sympathetic impulse, no sooner does sugar come in contact with the decaying gluten of the page 49 yeast than it becomes disturbed in its structure, and resolves itself into two bodies of simpler constitution and more stable character; for it is a general law in organic chemistry that when complex bodies change they do so into others of a simpler kind, the process being as it were a downward one, tending to reduce the substances changed more nearly to the comparative simplicity of the inorganic or mineral kingdom, from which they can be again elevated only by vegetable life under the restoring influence of the sun.

The products of ordinary fermentation, as the diagram shows, are alcohol and carbonic acid, the former remaining in the vat, the latter escaping. By passing the gas from the fermenting vat into lime-water it will be retained, and may be collected.

The alcohol remaining in the vat of fermented liquor imparts the stimulating and intoxicating property to it for which it is valued. Alcohol, though resembling water in appearance, differs physically in two points—it boils at a much lower temperature, and a gallon of it weighs 2 lbs. less than a gallon of water would. Hence, a liquor containing alcohol can have it readily separated by distillation. I have here a sample of liquor containing alcohol; I take a given quantity of it, for convenience sake say as much as will equal the bulk of 1000 grains of water; by now subjecting this to distillation I shall be quite sure all the alcohol will come over first; and by then weighing the product, and referring to certain tables, I shall ascertain precisely how much alcohol was contained in the liquor. This is the process always adopted to ascertain the strength of sweetened or mixed liquors. The process adopted by the Customs is to take what is termed a hydrometer, an instrument that partially sinks in water and spirit to a point proportionate to their gravity, the lighter and stronger the liquid the deeper the immersion, the degree being marked upon a scale attached.

We will now endeavour briefly to point out some of the properties of the products of fermentation.

Carbonic acid is, under ordinary conditions, an invisible gas, but may by pressure be liquified and even frozen. Being about half as heavy again as common air, it sinks in the latter, and may even be poured out of one vessel into another; and as it cannot support combustion, burning bodies are instantly extinguished when immersed in it.

It constitutes the "choke-damp" of miners, and is elimi- page 50 nated in vast quantities from volcanoes and certain mineral springs. It is the constituent which gives to lemonade, soda-water, bottled ale, and champagne their briskness, and is one of the final results of the combustion of fuels in open fires; also the matter into which a large proportion of the substances taken as food ultimately passes, being eliminated from the lungs in every expiratory breath.

Finally, carbonic acid is the main support and principal food of plants, being by them broken up into its constituents and reunited to other substances, such as nitrogen, hydrogen, phosphorus, and sulphur, ultimately reappearing in the form of grasses, fruits, trees, and flowers, for the use of the animal portion of organised creation, to give them food and life and enjoyment—to clothe the earth and fill it with beauty.

Alcohol, the other result of the process of ordinary fermentation, must now engage our attention. I have shown you how it may be separated from liquids containing it; let us now inquire into its properties. Here is a bottle containing some. A clear, colourless liquid, resembling water, very combustible, pleasant, and warm when drank; an agreeable perfume; very exhilarating; and in excess, intoxicating. When largely diluted it absorbs oxygen rapidly from the air, and becomes converted into acetic acid or vinegar. On the large scale this is effected by filling a vessel, having a false bottom, with some very porous material, such as beech wood chips, and pumping upon them very weak alcohol, and allowing it to percolate through the chips and out of the bottom of the cask, from which it is repeatedly returned. By this means, atmospheric air being freely admitted, oxygen is rapidly absorbed and vinegar produced.

As a lecture experiment platinum black may be taken instead of beech wood, as it still more rapidly causes the conversion of alcohol into acetic acid, readily shown by its action on litmus.

Alcohol is said to be the hydrate of a compound base termed ether, or one atom of ether combined with one atom of water; and under certain conditions, these bodies may be separated.

Ether is a remarkably volatile liquid, boiling at the temperature of the hand, and producing great cold upon the surface of the body it is leaving. Advantage has been taken of this property for the artificial production of ice, as in Harrison's patent, at present worked successfully in Victoria.

Ether is a base somewhat analogous in its chemical relations to the more fixed and durable alkalies and alkaline earths, and like them has the power of uniting with and neutralising acids producing characteristic compounds. We are thus introduced to a whole class of chemicals, many of them of a very interesting character. Its combination with hyponitrous acid is the origin of the "sweet spirits of nitre" of the shops, and is considered to resemble the flavour of apples. It is much used to impart flavour to the article known as imitation or artificial brandy.

With acetic acid it produces acetic ether, one of the ingredients also largely used to flavour artificial brandy. With butyric acid, one of the constituents of rancid butter and old cheese, it forms butyric ether, remarkable as proving to be identical with the peculiar flavouring principle of the pine-apple. If we distil alcohol with excess of sulphuric acid, we still further break it up and produce defiant gas. The flavour of various wines are due to the presence of a variety of vegetable ethers, produced by the slow and long-continued action of the acids contained upon the alcohol, especially when warmed; hence the bouquet and general improvement which good wines acquire by being long kept. Hence also the rawness, want of fragrance and flavour, usually noticed in very new wines.

To Pasteur belongs the credit of having discovered that wines may be artificially matured—that is to say, that the various flavouring ingredients and ethers may be easily developed by keeping wines for a certain time at a temperature of about blood heat. This discovery has been very useful to wine-makers and storers availing themselves of it.

The ether which more especially predominates in good wine, and as a consequence in good brandy too, is termed enanthic ether, and is a product of the action of tartaric page 52 acid upon alcohol in wine. It was originally discovered by Professor Liebig.

Most fermenting liquors contain, in addition to sugar, cellulose substances, such as the fibrous matters of grains and their skins, and, during the process of fermentation, especially if the temperature be somewhat high, and the solution free from acid, or still worse, alkaline, it has been found that the decomposition going on in the yeast and sugar becomes more or less communicated to them also. This need not surprise us, for when we reflect that these substances, however much they may differ in appearance, are composed of the same elements, as nearly as possible in the same proportions, it does not appear very wonderful that they should, under suitable conditions, be subject to the same sort of changes.

To those among you who may not be aware, I may as well state that there are in the vegetable world a number of very familiar substances so closely allied that chemists have termed them "isomeric"—that is to say, identical in composition, but different in form. Thus, in the class alluded to as concerned in fermentation, to which sugar belongs, we find gum, starch, cellulose (as in cotton wool), and cane and grape sugar; all these are as nearly as possible, if not absolutely identical in composition, and may indeed be often easily changed into one another. Thus, by long digestion in weak acid, starch becomes converted first into gum, and then into sugar; and if cotton wool or linen be subjected to the same treatment a sufficient length of time, the whole will disappear, and in their place a quantity of sugar, analogous to that found in fruits, will be formed.

In distilleries, where the object is to obtain the largest possible yield of alcohol from the saccharine materials, the process of fermentation is carried on to the uttermost, and not stopped as in brewing, before one-half of the sugar has been decomposed. Under these circumstances it is found that considerable quantities of cellulose become entangled in the peculiar decomposition of the ferments, and have imparted to them a similar decomposition. In this case, however, ordinary sugar alcohol is not produced, but instead we have a new body, possessing many of the physical properties of alcohol, but in other respects differing entirely. This new body is "fusel oil," so called from its somewhat insoluble character in water and oily appearance. When examined, fusel oil was found to have a somewhat similar page 53 relation to ordinary alcohol that the various sugars have to each other—members of the same family, having a family look, and partaking to a considerable extent of family peculiarities, but nevertheless distinct, and differing in character as much as brothers and sisters of ordinary human families usually do. True, the new body is a liquid, light and combustible, but boils at a heat exceeding that of alcohol. If we oxidise it we do not convert it into vinegar, but into a volatile acid possessing many of the leading qualities of acetic acid, yet altogether distinct. We produce valerianic acid, so called from it being always found among the class of plants called valerians, to which it imparts a peculiarly unpleasant smell. The root of the valerian officinalis particularly abounds in it, and is on that account used medicinally. A large class of valerianates are known, corresponding with the acetates, and like them always smelling of the acid. When we attempt to produce ethers from fusel oil, as in the corresponding alcohol series, still more startling discoveries are made, for when formed it has been found that the flavour of many fruits make their appearance; thus, with acetic acid an ether is formed, having the flavour in a highly concentrated degree of jargonelle pears, now much used to flavour sweetmeats. By varying the combinations several other flavouring essences have been produced having more or less similarity to well-known fruits. I have on the table essence of pine-apple, pear, black currant, cherry, apple, raspberry, all thus artificially prepared.

In the ordinary preparation of wines there are many circumstances which influence the result; thus, it has been found that if rapidly fermented, or at too high a temperature, a series of unpleasant ether's become formed in the wine, amongst which acetic ether is usually predominant, imparting that peculiar "mousey" flavour so often noticed in badly-made colonial wines.

There can be no question that the lower the temperature at which fermentation proceeds, and the more slowly it is effected, the better and more delicate will be the wine. It has even been found that the same grape-juice produces better wine when fermented in small vessels than when very large ones are used, the reason being that small bodies of liquid do not become so much heated as larger ones during fermentation, and also cool sooner afterwards. Even brewers have long been aware of this fact, and usually cool their fermenting liquors by means of spirals of cold water flowing through them.

The choicest Rhenish wines are made from grapes that grow in comparatively cold places, so that in point of fact they rarely ripen. Indeed it has been found that the best wines cannot be made in hot climates. In Europe, wines are often fortified and improved by boiling down the juice of the grape to a small quantity, and then mixing this concentrated syrupy extract with a portion of grape-juice not yet fermented; by this means greater body and sweetness become imparted to the mixed wine, and it loses a considerable proportion of the tartar so prevalent in many inferior wines. A reference to the chemical nature of tartar will explain this. This substance is a compound of tartaric acid and potash; it is not very soluble, requiring about 100 times its weight of cold water to dissolve it. Small as this quantity is, it becomes still less if alcohol be present; hence during the conversion of grape-sugar, in the process of fermentation, the wine becomes unable to retain the tartar in solution, and it becomes precipitated. An experiment will illustrate this.

My friend, Mr. Knight, who established a large vineyard at Riddell's Creek, informs me he can now make any kind almost of sweet liqueur wines, by previously in this manner concentrating his grape-juice. On one occasion, where the concentration had proceeded rather far, he was surprised to find the vessel in which it was stored nearly half-filled with crystals of tartar and other solid matters that had been deposited, the remainder of the liquor being a deliciously syrupy liquid, admirably adapted for fortifying and giving body to thinner varieties, and producing a wine less acid and better flavoured.

All fermenting liquids produce flavouring alcohols or fusel oils peculiar to themselves; and so persistent is the flavour thus often produced, that it cannot be got rid of. Whisky from malt, potato spirit, beetroot alcohol, arrack from rice, geneva from rye, and brandy from grapes, all have their peculiar flavours by which they may be distinguished; and by this means adulterations of the more expensive kinds may be detected. Simple evaporation upon the palm of the hand will often suffice. I have, in virtue of the difference existing in the various spirits, often detected the spurious Hamburgh wines, which used to be frequently imported here, and which were quite innocent of ever having seen a vineyard.

It has been found that in fermenting liquids, fusel oil is not produced, if certain aromatic substances, such as hops or page 55 cloves, be present, unless a very high temperature be used. Hence in well-made beer it ought not to be found. I have, however, often discovered it in colonial beers, especially some five years ago, when I undertook a series of examinations for the Royal Commission appointed to consider the Licensed Victuallers Act. Since this time, however, there have been numerous improvements in beer, and now, I believe, most of that sold, at any rate in Melbourne and suburbs and in the principal towns of Victoria, is good and wholesome.

Hops contain an aromatic volatile oil which may be separated by distillation from them. In the brewing of beer it is necessary to boil the hops. Now, it is quite possible to do this too much, so as to cause the evaporation and loss of oil of hops; hence when such wort comes to be fermented, it has lost much of the protecting ingredient that should prevent the formation of fusel oil. Thus it was that in years gone by many of the beers then made became thus contaminated with a disagreeable and unwholesome ingredient, recognised by connoisseur's as the "twang," so much complained of formerly in colonial beer. Since the period spoken of, however, our brewers have adopted a more rational process, and do not boil the hops so much as formerly.

Another cause for the occasional formation of fusel oil in beer is when the hop is only sparingly used, other bitters, such as quassia or gentian, being substituted.

Besides the ferments as yet spoken of, and so familiar to us in connection with bread, wines and beers, there exist in nature many other kinds of ferments; indeed their name is Legion.

All seeds owe their gemination and development into plants to a species of fermentation first set up in them.

A seed—say, for example, a bean—is composed of three essential parts—viz., the embryo, the radicle, and the cotyledons. The embryo is the future stem, the radicle is the destined root, and the cotyledons are storehouses of provisions.

When placed in a suitable place where it can grow—that is, under the influence of moisture and warmth—some peculiar changes commence. The cotyledons, which are filled mostly with starch and albuminous substances, begin to change—a ferment has been generated; the ferment slowly but surely converts the whole of the contained starch into sugar, which, being soluble in water, can be absorbed by the page 56 infant plant for its nourishment, and it begins to grow; if we may be allowed the comparison, it represents the mother's breast-milk to the young suckling.

We have here a beautiful illustration of that ever-to-be-found beneficent forethought of the Creator that never ceases to provide for the wants and preservation of all His creatures, in the storing away in the cotyledons of the seed of food in an insoluble form, so as not to be dissolved and washed away by the rains of winter, and only slowly altered as the needs of the growing plant may require it.

The process of malting is founded upon fermentation. Barley thrown into a heap, and moistened, begins to germinate. A ferment called diastase is formed in the gluten, by virtue of which much of the starch is converted into dextrine and sugar, and the plant begins to grow. When it has arrived at the proper stage of maturity, the vitality is destroyed by heating the grain over a kiln erected for the purpose, and we have malt. Malt, then, is simply barley that has germinated. When this malt is again wetted in the mash-tun during the process of brewing, at a temperature not too high, the ferment proceeds to complete the conversion of the remaining dextrine, and the whole becomes converted into sugar.

I have here an infusion of malt, and I wish to show you with what facility this conversion of starch takes place when the two are mixed.

All kinds of seeds are obliged to germinate in a manner corresponding with the before-going, in order that they may grow and develope their peculiarities. If an ordinary bitter almond, for instance, be examined, it will be found to have no smell until it is mixed with water and fermentation excited in it, when the peculiar flavour of bitter almond oil becomes at once apparent.

Bitter almonds contain a principle called amygdalin, which may be extracted from them by boiling alcohol, and it is to the decomposition of this substance under the influence of the ferment peculiar to almonds, that the new bodies are formed.

If amygdalin be rubbed in a mortar with water by itself, no change takes place, but it cannot be mixed with the fleshy part of an ordinary almond, even a sweet almond, without suffering decomposition.

If an ordinary sweet almond be rubbed up with water in one mortar, and some amygdalin in another, no effect is page 57 produced till they are mixed, when the smell of almonds is at once apparent. Ordinary table mustard has similar properties. Black mustard seeds, from which the best mustard is made, contain a principle corresponding to amygdalin called sinapin, and when treated like, the almond with water, the fleshy part of the seed at once sets up a fermentation, especially if warmed; and the result is that the sinapin, like the amygdalin, breaks up into several principles, among which the volatile oil of mustard, from its extreme pungency, is the most conspicuous. So long as the mustard is kept dry, no such change is produced.

Fermentation in the vegetable kingdom is much more common than may be supposed. It is, for instance, certain that to its influence the delicate perfumes arising from growing, and especially flowering plants, are to be referred. The (as yet) undeveloped bud contains the juices that upon the further opening of the flower are to commence to ferment by exposure to sunlight, warmth, and air; the results being, amongst other things, the sweet-smelling odours, and the honey which the busy bee so diligently collects.

If a handful of flower's—such as cowslip, violet, elder, or linden flowers—be placed in a fermenting liquor, the bouquet of the flower becomes communicated more strongly than could be effected by simply adding the distillate of one hundred times the amount, thus showing the marked effect of fermentation upon the juices of the flower; and it is said that advantage is often taken of this circumstance by vignerons to artificially impart some favourite bouquet to wines that only naturally are grown in some few favoured spots. It is said, on the authority of Liebig, that sage and rue are thus added, and thus some of the most celebrated wines imitated; but whilst, however, in the genuine product such flavour is permanent, the imitation is not so, but soon passes away. Brewers often take advantage of the same circumstance to impart a delicate hop flavour to beer by putting a few hand-fills of hops into each cask, to be filled with new beer that has not ceased fermenting.

It is well known to farmers that all old, well-stacked hay is sweeter and more relished by horses than new hay; also, that it has more fragrance or aroma. The cause is, that after it is stacked a species of fermentation sets in, the mass warms, and sugar and some flavouring ingredients are produced.

The very familiar article, "tea," is not sold in the condi- page 58 tion in which it is grown; if any person examines the leaves of the tea-trees to be found in our botanical gardens, he will be puzzled to trace any resemblance to ordinary tea, either in taste, smell, or colour. The peculiar properties of tea that render it so much esteemed do not exist in the growing plant, but are produced by subjecting the leaves to a peculiar fermentation during the process of drying.

The green leaf of tobacco, again, possesses none of the well-known properties of ordinary smoking tobacco; these are, as in tea, all developed by fermentation during the process of drying.

The ripening of fruits is the result of a fermentative process by which the starch so largely contained in all green fruits becomes converted into sugar.

In the animal economy the process of digestion is referable to a fermentative principle, "pepsine," present in the stomach, and the action of rennet upon milk in cheese-making is produced by the same substance, rennet being only the stomach of a calf cleaned and preserved. Dyspepsia is often only fermentation in the stomach. The difference between new and old cheese is the result of fermentation; indeed, a cheese that is quite new has no flavour whatever, consisting simply of curds and salt; but after it has been placed in the ripening-room a certain time, the new cheese warms, ferments, and develops the well-known flavour of cheese. The souring of milk is due to a species of ferment called lactic acid. Even hams and bacon undergo a peculiar ripening flavour by being kept, not existing in them when in the green state; and the longer they are kept the more pronounced does it become, and the more valuable the ham, so long as it is not allowed to become rancid. The Westphalian hams imported into England were remarkable examples of this extreme development of flavour without rancidity. Most of our colonial hams are little better than dried salt pork, and are singularly destitute of that rich flavour one was accustomed to find in Cumberland or Yorkshire hams. I am told that the climate has much to do with this, the best results being obtained in cold climates and very slow processes.

The changes which the best fresh butter suffers by keeping are induced in it principally by the fermentation of the milk not perfectly extracted from it, and it has been found that if required to be long kept, great precautions are necessary to effect the complete removal of the latter sub- page 59 stance. Here, again, climate interferes, as it is much easier to separate milk perfectly from butter in cold than in warm climates; England, Ireland, and New Zealand will always therefore have advantages over Victoria in the perfecting of their dairy produce.

It is now well understood that many diseases which flesh is heir to are produced by various ferments. That terrible one known as diabetes is an instance in point. In this case a certain diseased organ of the body cannot come into contact with starch without immediately converting it into sugar; the two bodies excite each other to increased action; hence, to effect a cure or an alleviation of this malady, it is customary to recommend abstinence from all food containing starch; such fermentation being thus prevented in the body, the diseased organ is not excited, but has a chance, with treatment and care, of casting off the diseased condition, and becoming again healthy.

All contagious and infectious diseases are now referred to the action of ferments of similar kinds, communicated from one diseased individual to another previously in good health, and that in these cases the peculiar disease is always reproduced, with all its old symptoms and characters, to be again propagated, if opportunity offers, amongst fresh subjects.

We will now, before concluding, devote a few minutes to the causes of fermentation as now understood by philosophers.

To Schulze and Schwann the credit belongs of having first pointed out that if, before admitting air to a body capable of fermentation, that air be first passed through a red-hot tube, no fermentation was produced, and this led to the belief that the atmosphere contained germs or seeds which, becoming deposited upon suitable substances, set them fermenting by establishing a growth. Many close observers have since then, by means of the microscope, established the presence of such growths in fermenting bodies. Helmholtz went further, and showed that by separating a fermenting liquid from one not undergoing that change, by means of a membrane, such as a piece of bladder, porous enough to allow the fluid to pass through and become intermixed, but stopping the passage of solids, the fermentation process was not communicated through; therefore the cause of the development of fermentation in a suitable liquid must lie in something which cannot pass through membrane. He therefore naturally attributed it to some solid substances.

Since then Schroeder and Dusch ascertained that these germs might be separated from air by simply filtering it through cotton wool, but it was left to Professor Tyndall finally to clear up the point, he has demonstrated that ordinary air, to rise the words of Professor Huxley, is no better than a sort of stirabout of excessively minute solid particles; that these particles are almost wholly destructible by heat, and that they are strained off, and the air rendered optically pure, by being passed through cotton wool.

To Pasteur, however, belongs the distinguished honour of having proved that germs really are filtered out by the cotton wool from air, for upon subjecting to microscopic investigation, he detected germs in the matter so filtered, and proved their power to excite fermentation when simply sown in a solution fit for their development.

Surgeons have long been aware of the danger of allowing air to gain admission into wounds, which would then fester and give rise to the most alarming symptoms, the germination of spores thus gaining admission being the cause. The beneficial effect of cotton wool as an external application to burns and scalds can now also be understood.

Pasteur not only ascertained that sperms were constantly floating about the air, but he also discovered that they abounded more in some places than in others, being plentiful in plains, and diminishing in number at great altitudes, as on the sides of mountains. I do not remember whether Pasteur carried on his observations at sea also, but the well-known length of time that meat keeps when hung up to the rigging of vessels may be due in some measure to the comparative absence of spores in sea air.

My own personal observations have shown to me that these germs are very numerous in forests, and on several occasions when I have taken a tent and camped for a few days near Fern-tree Gully, amongst the Dandenong Ranges, I have always found that meat very rapidly became putrid, unless salted; and, upon inquiry, I ascertained this to be the experience also of the settlers in the neighbourhood.

There can be no doubt that ordinary butchers' meat keeps longer when due regard has been paid to cleanliness, both in the abattoirs and in the places where it is subsequently stored.

It is also well understood that many diseases are largely propagated in consequence of the gross neglect of cleanliness amongst the inhabitants of certain districts, for every bit of page 61 organic dirt allowed to lie about and putrefy becomes the centre and source of millions of spores, ready to be diffused around, or, as very sensibly suggested by Dr. M'Crea, the Chief Medical Officer, perhaps carried by flies to fresh and even distant subjects. By no other means, indeed, could the somewhat recent appearance of small pox in different places be accounted for.

Plants are also subject to the attacks of germs, and it cannot be doubted that smut in wheat, and the grape disease, and potato disease, are produced thereby.

It appears that insects are peculiarly liable to these attacks. In autumn, may often be seen upon windows dead flies, surrounded by a sort of white, woolly substance. Upon examination it has been found that the white substance consists of innumerable spores cast off in all directions by a minute fungus called "empusa musa," the spore-forming filaments of which stand out like a pile of velvet from the body of the fly, whilst the roots have taken complete possession of the fly's body.

The silkworm has long been known to be subject to a very fatal contagious and infectious disease called the "muscardine;" this disease is entirely due to a fungus. But of late years a still more serious disease has broken out amongst the silkworms, called the "pebrine," and has proved so destructive that it is estimated that the direct loss to France alone, in seventeen years, cannot be less than 50 millions sterling, to say nothing of the indirect loss caused by stoppage of looms and loss of employment.

In 1858 the gravity of the situation caused the French Academy of Sciences to appoint commissioners to devise some method of stopping, if possible, the plague. Some naturalists took one view and some another, till at last the French government despatched Pasteur to study it, which he did most perfectly and completely, the result being that the cause was again assigned to germs of a peculiar kind. As might indeed be imagined from his previous training, Pasteur was early led to suspect the true nature of the malady, and of devising a method of extirpating the disease, which has proved to be successful wherever it has been properly carried out.

I shall conclude this lecture by quoting the words of Professor Huxley, at the conclusion of his inaugural address at the meeting of the British Association, hold at Liverpool, September 14th, 1870;— page 62

"Looking back no further than ten years, it is possible to select three—1863, '64, and '69—in which the total number of deaths from scarlet fever alone amounted to 90,000; that is the return of killed, the maimed and disabled being left out of sight. Why, it is to be hoped that the list of killed in the present bloodiest of wars will not amount to more than this! But the facts which I have placed before you must leave the least sanguine without a doubt that the nature and the causes of this scourge will one day be as well understood as those of the pebrine are now, and that the long-suffered massacre of our innocents will come to an end.

"And thus mankind will have one more admonition that 'the people perish for lack of knowledge,' and that the alleviation of the miseries and the promotion of the welfare of men must be sought by those that will not lose their pains in that diligent, patient, loving study of all the multitudinous aspects of nature, the results of which constitute exact knowledge or science."