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, o.1 gm. 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.

I

Pasteur, L., Annal. d. Chim. et d. Physique, 1862, 3 sér., lxiv., 1.

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.

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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,' sulphur and perhaps also on iron bacteria have to all appearances pointed a way out of this difficulty. It

I

Winogradsky, S., "Die Nitrification," Handb. d. tech. Mykol., 190406, iii., 132.

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; I gm. ammonium sulphate, I gm. potassium phosphate, I gm. magnesium carbonate, to I 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 CO, 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." "Since the oxidation of NH, is the only source of chemical energy which the nitrifying • Winogradsky, loc. cit., p. 163 and ff.

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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.

It is obvious that I 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.'

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

I Godlewski, E., Anz. d. Akad. d. Wissersch. in Krakau, 1892, 408; 1895, 178.

the hydrogen sulphide which is formed as a reduction product from CaSO, 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, according to the scheme:

The sulphuric acid is at once neutralized by carbonates.

Winogradsky assumes that the oxidation of HS by the sulphur bacteria is the source of energy which plays the same rôle as the oxidation of NH, plays in the nitrifying bacteria, or the oxidation of carbon compounds -sugar and others-in the case of the other lower and higher organisms. Winogradsky has made it very probable that sulphur bacteria do not need any organic compounds and that their nutrition may be accomplished with a purely mineral culture medium, like that of the nitrite bacteria. On the basis of this assumption they should also be able to form sugars from the CO, of the air.

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Nathanson discovered in the sea water the existence

'Nathanson, Mitteil. d. zool. Station, Neapel, 1902.