mon to certain metals and their oxides. Bredding and Von Bermaik showed that a gramatomic weight (193 grams) of colloidal platinum diffused through 70,000,000 litres of water shows a perceptible reaction on more than 1,000,000 times the quantity of hydrogen peroxide; and H. C. Jones demonstrated that the reduction that here takes place is a monomolecular reaction. Curiously enough, the analogy between the action of such metallic solutions. and that of the enzyme goes further. Finely divided platinum, palladium, iridium, osmium, etc., thus have the power of inverting cane sugar, like one of the enzymes-invertase; and certain poisons, such as hydrocyanic acid, sulphuretted hydrogen, carbon disulphide and mercuric chloride, which inhibit or even suspend the action of the enzymes entirely, exert a similar influence upon the solution of colloidal platinum." (1)

Unfiltered grape juice, when set aside in a containing vessel under favorable influences of temperature, will soon undergo fermentation. The grape juice, at first clear, will soon become turbid and actively agitated by escaping carbon dioxide. Physical and chemical changes take place. Microscopically, it may be seen to contain numbers of ferment cells; chemically, it shows that the grape sugar has in considerable part been destroyed, and that an entirely new substance, alcohol, has been produced. Finally, when the process of fermentation has ceased, there may yet remain sugar in the fermenting fluid capable of being decomposed, and ferment cells capable of decomposing it. Alcohol, the principal product of vinous fermentation, is the substance that causes this arrest of fermentation. It stands, as it were, between the sugar on one side and the yeast cells on the other, prevents the one from decomposing the other, and is therefore an antibody to vinous fermentation. Remove the alcohol, and fermentation again begins; and it again ceases as soon as the requisite per cent of alcohol has again accumulated. Thus the process may be continued until all the sugar is decomposed, or it will be permanently arrested by allowing the alcohol to remain. In the latter case the wine fermented is

the sweet variety; when the sugar is entirely decomposed, the variety is a sour wine.

The chief points of difference between the two classes of ferments are indicated by the names living and non-living.

Living ferments are living cells which have the capacity of growing, of assimilating, of reproducing, of decomposing, and of transforming fermentable substances into ferment products; enzymes, or non-living ferments, can neither grow, assimilate, nor multiply themselves, but they possess, in common with the other class, the capacity of decomposing and transforming fermentable substances into ferment products.

It is a well established fact that the capacity of a living ferment to do specific ferment work, that is, to bring about the decomposition of fermentable substances and the recombination of the dissociated atoms into ferment products, can be modified so that the specific activity of the ferment can be increased or decreased temporarily or permanently at the will of the operator; or by natural causes. And it has been further shown that these modifications do not visibly influence the cell in its vital characteristics, and that qualities thus acquired may be transmitted by the cells to their progeny. The cell will continue to grow, to assimilate, and to multiply itself as before, notwithstanding that its capacity to do specific work will have been modified more or less permanently, or totally destroyed, and this modification may be transmitted by inheritance. It will appear from these facts that the vital or vegetative functions of a ferment cell are quite different from those which give the cell its capacity to do specific ferment work.

It was shown by Pasteur, and later confirmed and more fully worked out by Hansen, that a pure culture of ferment micro-organism is necessary in order to secure purity in sacchariferous fermentations. The quality of beer, for example, has been greatly improved by methods in securing pure cultures of the required ferment. More recently "Emil Fischer has, by purely chemical research resulting in his celebrated work on the synthesis of sugars, on the use of phenyl-hydrazin and on the azone reaction, diverted

the current of views on fermentation pehenomena into new channels. His researches led him to explain the behavior of yeast towards the particular sugar of the nutritive liquid in the same way as the action of the enzyme (invertase emulsin) so that the chemical activity of the living cell does not differ from the action of chemical ferments.

According to Fischer the fermentation of polysaccharides is always preceded by the hydrolysis of sugar. But there exists an exact relation between the molecular structure of a given sugar and the sugar inverting enzyme of the yeast cell; if the sugar comes into contact with the albuminoids of the yeast cell, which play the most important part among the agents of which the living cell makes use, the sugar is decomposed only if the configuration, the geometrical structure of its molecules, does not deviate too much from the configuration of the molecules of the albuminoids."

Furthermore, Buchner has recently shown that the juice obtained from the yeast cells by hydraulic pressure is capable of quickly fermenting highly concentrated sugar solutions of various kinds, even after it has passed through a Birkefeld filter. He infers from his experiments that the fermentative power of the expressed juice is embodied in a soluble enzymelike substance isolated from the living cell plasma.

However, it has been demonstrated repeatedly by independent observers that a vessel filled with unfiltered grape juice and divided into two parts by a thin layer of cotton wool, shows active fermentation only in that portion in which yeast cells are introduced. Since such a partition is incapable of prohibiting the free passage of soluble enzymes, we must conclude that the direct contact of the yeast with the fermentable substance is necessary. In other words, it has been shown that the active cause of fermentation is a substance which is not normally thrown off by the cells, but which may be extracted from them by destroying the inherent properties of the cells, including their vitality. That the function.

*Italics author's.

of vitality is not identical with that of fermentation is proved by the facts of attenuation already mentioned. I conclude, therefore, that the active ferment is not a secretion of the ferment microorganism, but is an inherent property of the cell which may be destroyed, but not extracted without destroying the vitality of the micro-organism.

It may be well to keep in mind the fact that the products of fermentation inhibit the activities from which they result. Alcohol, for example, inhibits vinous fermentation, when its accumulation in the solution has reached a definite combination. When this equilibrium is reached, the sugar is immune to the activities of the yeast cell, and alcohol is the immunizing agent. This is not a phenomenon characterizing vinous fermentation alone, but is, on the contrary, common to all fermentations. Nor is it a chemical combination between the factors involved, but must be a physical equilibrium (if I may use the term), because of the fact that the removal of a portion of the alcohol results in fermentation again becoming active until the requisite percentage of alcohol has again accumulated.

INFECTION AND IMMUNITY.

The phenomena of infection and immunity have been so thoroughly discussed in recent literature that it becomes unnecessary to do more than mention the more characteristic features of these processes.

INFECTION.

Infection may be defined as that condition of the body resulting from the entrance and the multiplication of micro-organisms which cause to be produced organic poisons whose effects upon the organism are the symptoms of disease. The introduction of pathogenic products alone may cause symptoms and lesions of infection, but the resulting condition in this case is not communicable; as the presence of living pathogenic microbes is necessary to the possession of this latter quality.

The following characteristics are possessed in common by patho

genic and ferment micro-organisms. (1) They are specific in their activities. (2) The power possessed by ferment micro-organisms to produce specific ferment products is manifested by pathogenic micro-organisms as a power to produce specific pathogenic products; but the results obtained with either species of microorganism, ferment or pathogenic, will vary with the environmental conditions of heat, soil, light, etc., under which the micro-organisms are placed. (3) With both species the capacity of the microorganism to do specific work, as fermentation in the one instance and pathogenesis in the other, may be modified, lessened or increased temporarily or permanently, without visibly changing the vital characteristics of the micro-organism whereby it lives, grows, assimilates and propagates. (4) It has been shown that the function of cell vitality, of both species of micro-organisms, is not identical with the capacity of the cell to do specific workferment or pathogenic-and that the latter function is an inherent property which can be variously modified or destroyed by natural or by artificial means, but which can not be extracted without destroying the vitality of the cell. (5) The products of cell activities-ferment and pathogenic-are inhibitory substances, antibodies, which tend by accumulation to arrest the processes of which they themselves are the results.

IMMUNITY.

Immunity of an organism to infection may be an acquired or a congenital condition. Once acquired immunity may be partial or complete, temporary or permanent. The means of defense against infection which an organism acquires is not the same in all cases. In one form of acquired immunity the organism is capable of neutralizing the toxins, antitoxic immunity. In another form of immunity the organism is able to destroy the invading bacteria, antibiotic immunity. In another form of acquired immunity the protection enjoyed by the organism is due to conditions which prevent the production of toxins in its tissues by a species of pathogenic bacterium. This form I will call somatic immunity. But since