organism and a crystal are merely superficial and it is by pointing out the fundamental differences between the behaviour of crystals and that of living organisms that we can best understand the specific difference between non-living and living matter. It is true that a crystal can grow, but it will do so only in a supersaturated solu­tion of its own substance. Just the reverse is true for living organisms. In order to make bacteria or the cells of our body grow, solu­tions of the split products of the substances composing them and not the substances themselves must be available to the cells; second, these solu­tions must not be supersaturated, on the contrary, they must be dilute; and third, growth leads in living organisms to cell division as soon as the mass of the cell reaches a certain limit. This process of cell division cannot be claimed even metaphorically to exist in a crystal. A correct apprecia­tion of these facts will give us an insight into the specific difference between non-living and living matter. The forma­tion of living matter consists in the synthesis of the proteins, nucleins, fats, and carbohydrates of the cells, from the split products. To give an historical example, Pasteur showed that yeast cells and other fungi could be raised on the following sterilized solu­tion: water, 100 gm., crystallized sugar, 10 gm., ammonium tartrate, 0.2 gm. to 0.5 gm., and fused ash from yeast, 0.1 gm.7 He undertook this experi­ment to disprove the idea that protein or organic matter in a state of decomposi­tion was needed for the origin of new organisms as the defenders of the idea of spontaneous genera­tion had maintained.

2. That such a solu­tion can serve for the synthesis of all the compounds of living yeast cells is due to the fact that it contains the sugars. From the sugars organic acids can be formed and these with ammonia (which was offered in the form of ammonium tartrate) may give rise to the forma­tion of amino acids, the “building stones” of the proteins. It is thus obvious that the synthesis of living matter centres around the sugar molecule. The phosphates are required for the forma­tion of the nucleins, and the work of Harden and Young suggests that they play also a rôle in the alcoholic fermenta­tion of sugar.

Chlorophyll, under the influence of the red rays of light, manufactures the sugars from the CO₂ of the air. This makes it appear as though life on our planet should have been preceded by the existence of chlorophyll, a fact difficult to understand since it seems more natural to conceive of chlorophyll as a part or a product of living organisms rather than the reverse. Where then should the sugar come from, which is a constituent of the majority of culture media and which seems a prerequisite for the synthesis of proteins in living organisms?

The investiga­tions of Winogradsky on nitrifying,8 sulphur and perhaps also on iron bacteria have to all appearances pointed a way out of this difficulty. It seemed probable that there were specific micro-organisms which oxidized the ammonia formed in sewage or in the putrefac­tion of living matter, but the attempts to prove this assump­tion by raising such a nitrifying micro-organism on one of the usual culture media, all of which contained organic compounds, failed. Led by the results of his observa­tions on sulphur bacteria it occurred to Winogradsky that the presence of organic compounds stood in the way of raising these bacteria, and this idea proved correct. The bacteria oxidizing ammonia to nitrites were grown on the following medium; 1 gm. ammonium sulphate, 1 gm. potassium phosphate, 1 gm. magnesium carbonate, to 1 litre of water. From this medium, which is free from sugar and contains only constituents which could exist on the planet before the appearance of life, the nitrifying bacteria were able to form sugars, fatty acids, proteins, and the other specific constituents of living matter. Winogradsky proved, by quantitative determina­tion, that with the nitrifica­tion an increase in the amount of carbon compounds takes place. “Since this bound carbon in the cultures can have no other source than the CO₂ and since the process itself can have no other cause than the activity of the nitrifying organism, no other alternative was left but to ascribe to it the power of assimilating CO₂.”9 “Since the oxida­tion of NH₃ is the only source of chemical energy which the nitrifying organism can use it was clear a priori that the yield in assimila­tion must correspond to the quantity of oxidized nitrogen. It turned out that an approximately constant ratio exists between the values of assimilated carbon and those of oxidized nitrogen.” This is illustrated by the results of various experi­ments as shown in Table I.

TABLE I

It is obvious that 1 part of assimilated carbon corresponds to about 35.4 parts oxidized nitrogen or 96 parts of nitrous acid.

These results of Winogradsky were confirmed in very careful experi­ments by E. Godlewski, Sr.10

The nitrites are further oxidized by another kind of micro-organisms into nitrates and they also can be raised without organic material.

Winogradsky had already previously discovered that the hydrogen sulphide which is formed as a reduc­tion product from CaSO₄ or in putrefac­tion by the activity of certain bacteria can be oxidized by certain groups of bacteria, the sulphur bacteria. Such bacteria, e. g., Beggiatoa, are also commonly found at the outlet of sulphur springs. They utilize the hydrogen sulphide which they oxidize to sulphur and afterwards to sulphates,