This does not, however, dispose of the statement that the action of the digestive and alcoholic ferments is quite opposite in character, nor can I see how this contention can be upheld. Ferments were at one time divided into those which were structureless, lifeless, amorphous substances, termed enzymes, and those which were living organisms with a definite structure. To the former class belonged all the digestive ferments, such as diastase, maltase, amylase, etc, and to the latter such substances as yeast. It was then considered that their mode of action was essentially different, although their ultimate results were similar or identical. It is now known that organised ferments are simply a residence for the unorganised ferments, and that their action is entirely dependent on the latter, although there is no sharp line of demarcation between individual cell-ferments and the free unorganised ferments. It is recognised, however, that there are decided differences between them, as for example, that the organised ferments are easily destroyed, being killed by oxygen under pressure, and rendered inoperative by a temperature of 100° F., while many antiseptics, e.g., salicyclic acid and chloroform, paralyse their activity. Unorganised ferments, on the other hand, are not affected in their action by chloroform, and resist when dry a much higher temperature, although in solution they are decomposed quite as easily as their organised allies; but probably these differences are more apparent than real, and owe their origin to the accidental circumstance of association with living protoplasm.

Fermentation has been defined as the chemical change produced by the agency of protoplasm, or of a secretion prepared from it, the former class being exemplified by the lactic acid fermentation of sugar and the acetic acid fermentation of alcohol, whilst the alcoholic fermentation of sugar is a typical example of the latter class. By mixing brewer's yeast with quartz, sand, and infusorial earth, grinding the resulting mass and subjecting it to a pressure of 400 to 500 atmospheres, Buchner was able to extract a substance called zymase, which could decompose sugar into carbonic acid and alcohol. It is perhaps more correct to say that the liquor expressed from yeast contains the enzyme zymase, an unorganised ferment which is responsible for the alcoholic fermentation. As this yeast juice is difficult to prepare and rapidly loses its activity on standing, a preparation termed zymin, or permanent yeast, is now used, which will retain its active properties for a prolonged period. It is a dry powder, consisting of yeast cells which have been killed by contact with ether-alcohol or ether-acetone, but still containing the active enzyme (zymase).

The yeast cell contains several ferments, amongst them being invertase, an enzyme capable of passing through the cell wall, and thus termed an extra-cellular enzyme, in contradistinction to maltase and zymase, which are intra-cellular, as they can only be obtained by breaking down the cell wall wholly or partially. Maltase and invertase are identical with the normal digestive ferments of the same name. In addition to this, however, the liquor expressed from the yeast cells contains a ferment called endotryptase, whose action quickly counteracts and destroys zymase.

In spite of much careful research, very little is yet known of the ferments or, as they are now more usually designated, enzymes. Information is, however, being slowly accumulated which tends to relate them to the proteins, and the following outstanding facts regarding them and their effects are worthy of mention: -

(1) Their activity involves no change in themselves, and an absurdly attenuated quantity can repeat the same reaction over and over again. It is known that invertase can invert 200,000 times its own weight of cane sugar and rennin double that quantity of casein. (2) Their action is by no means unlimited, because in course of time a gradual loss of efficiency betrays itself. (3) Their operations are absolutely specific, fats, carbohydrates, and proteins being acted upon by distinctive enzymes capable of effecting changes in themselves alone. The nature of the reactions are inferred from the end-products, which are in most cases recognisable. (4) For the most part ferments are produced in the body by living cells, some of them being retained in substance of the cells for their own personal ends and others expelled for purposes directly or indirecf.ly to benefit them. (5) Ferments have many analogies with toxins. Injected subcutaneously, they act as poisons, producing a rise of temperature and finally death, while, as we have seen, anti-ferments can be formed in the same way as antitoxins.

It is now known that micro-organisms do not effect their deleterious action upon the body per se, but through the medium of their exudations, and as these are mostly of the nature of enzymes, the germ theory of disease itself is closely bound up with fermentation. Many of their products, such as ptomaines and toxins, are of the most poisonous character, and it is interesting to know that while the former are alkaloidal, the latter are proteins with no really essential chemical differences from those which are useful as foods.

The enzymes may be classified as: -

(1) Hydrolytic, including those which induce the substance on which they act - termed the substrate - to combine with water before disintegration. All the digestive enzymes are of this character, and these may be arranged as follows: - (a) amylolytic or saccharolytic, which convert polysaccharides into dextrose, e.g., ptyalin, amylopsin; (b) inverting, which convert disaccharides into monosaccharides, e.g., invertase, maltase, lactase; (c) lipolytic, which split fats into fatty acids and glycerine, e.g., lipase; (cl) proteolytic, which split proteins into proteoses, peptones, polypeptides, and amino-acids, e.g., pepsin and trypsin; (e) peptolytic, which split proteoses and peptones into polypeptides and amino-acids, e.g., erepsin.

(2) Oxidising ferments, e.g., oxidases, which are mainly intracellular and oxygen carriers.

Other-excellent examples of intracellular enzymes are to be found practically in every cell, and are intimately associated with metabolic changes in the protoplasm. Their action is chiefly digestive in character, and as their activity continues after death, they are responsible for autolysis when the tissues are kept in an aseptic condition and at an appropriate temperature.

Observations on the cells of many secreting organs disclose little granules, which are really the precursors of the enzymes, hence called zymogens. Many of these are at once expelled from the cells as active enzymes, but some few require the co-operation of a specific activating agent before they can be converted into effective ferments. Trypsinogen, which is an excellent illustration of this class, requires the intervention of enterokinase, itself an enzyme, and hence called the enzyme of enzymes, or mother of ferments, by Pavlov.

Under special conditions many enzymes are capable of reversing their usual activity. Thus, instead of the substrate being converted into its usual end-product, this latter may become the substrate, and produce the former as its end-product - a condition termed reversible zymolysis.

It has not yet been demonstrated that the digestive ferments are capable of converting sugar into carbonic acid and alcohol, but the saccharolytic enzymes are quite capable of effecting this result. These are of two kinds, the former, sucrase or invertase, isolated by Berthelot, and capable of converting cane sugar into glucose; the latter, alcoholase, identical with the zymase obtained from yeast by Buchner, which splits the glucose into alcohol and carbonic acid. Besides which, Professor W. E. Dixon, of Cambridge, has shown that the bacillus coli can produce from 9 to 17 per cent. of alcohol when allowed to grow in sugar, and it is fair to suppose that as this action must take place in the colon, the alcohol so produced must pour into the system.

Hence, without the effect of living yeast cells, we are all alike subject to the results of the activities of quite similar ferments in the body, and, in fact, the action of the digestive and alcoholic ferments is practically identical. The minute quantity of alcohol contained in ordinary bread may therefore be safely ignored when we reflect on the probable amount that may be manufactured in the alimentary canal quite outside of our own control.

But if further evidence were necessary of the innocuous nature of yeast, it is to be found in the series of experiments conducted upon rats by Professor Leonard Hill in connection with the controversy on the respective nutritive values of white and standard bread. The yeast employed in the manufacture of standard bread manifestly exerted no deleterious action on the rats, which flourished equally exuberantly under the nourishing influence of standard bread or standard flour. The fact that growth was stimulated to a like extent both by the flour and the bread is a sufficient indication that not only was the yeast harmless, but that its influence was a negligible quantity. It is perhaps rather unfortunate that this should be the case, as yeast is a substance rich in the organic compounds of phosphorus to such an extent that, as has already been mentioned, it can prevent the development of polyneuritis in animals fed upon rice, barley, and wheat flour in which the outer layer of the grain has been removed in milling, and where the disease is present its timely administration can cure it.

On the other hand, the effort to obviate any waste in the preparation of bread is entirely praiseworthy, although one may safely conjecture that when all precautions have been taken a certain percentage of waste is likely to arise. In yeast-raised bread, that which is associated with the conversion of a small proportion of the sugar is quite unavoidable, and to this extent the yeast-free bread is so much the more nutritious. On account of its close texture, it also compels much more careful mastication, although it is hardly likely to call forth such a large quantity of "appetite juice," until one has become accustomed to its use. Its devotees, however, appear to appreciate both its nutritive qualities and its flavour, and declare that "by taking unfermented food and by abstaining from the opposite, their sense of smell becomes regenerated, and the odour of putrescence inseparable from yeast is recognised as the odour of disease, and they can no longer endure to be in its presence." This statement is clearly the outburst of a zealot, because outside of a bakery it is quite impossible to detect the odour of yeast in association with well baked bread. The impossibility of swallowing the so-called "starvation compounds" of the ordinary baker is purely a psychical effect, and as such explicable on other grounds than those which appeal to the senses.

We are bound to commend these propagandists, however, for their effort to produce a pure bread, made from washed wholemeal, finely ground, devoid of salt or other chemicals, and would recommend the ordinary baker to emulate them in such a desirable attainment. This would clearly lead to the more careful mastication and insalivation of bread, and by bringing the other items of food into harmony would unquestionably tend to inculcate the principle of moderation.