according to the scheme:

The sulphuric acid is at once neutralized by carbonates.

Winogradsky assumes that the oxida­tion of H₂S by the sulphur bacteria is the source of energy which plays the same rôle as the oxida­tion of NH₃ 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 CO₂ of the air.

Nathanson11 discovered in the sea water the existence of bacteria which oxidize thiosulphate to sulphuric acid. They will develop if some Na₂S₂O₃, is added to sea water. These bacteria can only develop if CO₂ from the air is admitted or when carbonates are present. For these organisms the CO₂ cannot be replaced by glucose, urea, or other organic substances. Such bacteria must therefore possess the power of producing sugar and starch from CO₂ without the aid of chlorophyll. Similar observa­tions were made by Beijerinck on a species of fresh-water bacteria.12

Finally the case of iron bacteria may briefly be mentioned though Winogradsky’s views are not accepted by Molisch.

We may, therefore, consider it an established fact that there are a number of organisms which could have lived on this planet at a time when only mineral constituents, such as phosphates, K, Mg, SO₄, CO₂, and O₂ besides NH₃, or SH₂, existed. This would lead us to consider it possible that the first organisms on this planet may have belonged to that world of micro-organisms which was discovered by Winogradsky.

If we can conceive of this group of organisms as producing sugar, which in fact they do, they could have served as a basis for the development of other forms which require organic material for their development.

In 1883 the small island of Krakatau was destroyed by the most violent volcanic erup­tion on record. A visit to the islands two months after the erup­tion showed that “the three islands were covered with pumice and layers of ash reaching on an average a thickness of thirty metres and frequently sixty metres.”13 Of course all life on the islands was extinct. When Treub in 1886 first visited the island, he found that blue-green algæ were the first colonists on the pumice and on the exposed blocks of rock in the ravines on the mountain slopes. Investiga­tions made during subsequent expedi­tions demonstrated the associa­tion of diatoms and bacteria. All of these were probably carried by the wind. The algæ referred to were according to Euler of the nostoc type. Nostoc does not require sugar, since it can produce that compound from the CO₂ of the air by the activity of its chlorophyll. This organism possesses also the power of assimilating the free nitrogen of the air. From these observa­tions and because the Nostocaceæ generally appear as the first settlers on sand the conclusion has been drawn that they or the group of Schizophyceæ to which they belong formed the first settlers of our planet.14 This conclusion is not quite safe since in the settlement of Krakatau as well as in the first colonizing of sand areas the nature of the first settler is determined chiefly by the carrying power of wind (or waves and birds).

We may now return from this digression to the real object of our discussion, namely that the nutritive solu­tions of organisms must be very dilute and consist of the split products of the complicated compounds of which the organisms consist. The examples given sufficiently illustrate this statement.

The nutritive medium of our body cells is the blood, and while we take up as food the complicated compounds of plants or animals, these substances undergo a diges­tion, i. e., a splitting up into small constituents before they can diffuse from the intestine into the blood. Thus the proteins are digested down to the amino acids and these diffuse into the blood as demonstrated by Folin and by Van Slyke. From here the cells take them up. The different proteins differ in regard to the different types of amino acids which they contain. While the bacteria and fungi and apparently the higher plants can build up all their different amino acids from ammonia, this power is no longer found in the mammals which can form only certain amino acids in their body and must receive the others through their food. As a consequence it is usually necessary to feed young animals on more than one protein in order to make them grow, since one protein, as a rule, does not contain all the amino acids needed for the manufacture of all the proteins required for the forma­tion of the material of a growing animal.15

3. The essential difference between living and non-living matter consists then in this: the living cell synthetizes its own complicated specific material from indifferent or non-specific simple compounds of the surrounding medium, while the crystal simply adds the molecules found in its supersaturated solu­tion. This synthetic power of trans­forming small “building stones” into the complicated compounds specific for each organism is the “secret of life” or rather one of the secrets of life.

What clew have we in regard to the nature of this synthetic power? We know that the comparatively great velocity of chemical reac­tions in a living organism is due to the presence of enzymes (ferments) or to catalytic agencies in general. Some of these catalytic agencies are specific in the sense that a given catalyzer can accelerate the reac­tion of only one step in a complicated chemical reac­tion. While these enzymes are formed by the action of the body they can be separated from the body without losing their catalytic efficiency. It was a long time before scientists succeeded in isolating the enzyme of the yeast cell which causes the alcoholic fermenta­tion of sugar; and this gave rise to the premature statement that it was not possible to isolate this enzyme since it was bound up with the life of the yeast cell. Such a statement was even made by a man like Pasteur, who was usually a model of restraint in his utterances, and yet the