Page:Life and death (1911).djvu/188

 *stituent cells it is the exclusive substance of Primus; and, in the same way, the living matter of another individual Secundus will carry everywhere his personal impress, which differs from that of Primus.

But it is none the less true that this absolute specificity is based with certainty only on differences which from the chemical point of view are exceedingly slight. All these protoplasms have a very analogous composition. And, if we regard as negligible the smallest individual, specific, generic, or ordinal variations we may then speak in a general manner of protoplasm or living matter.

Experiment shows us, in fact, that the real living substance—apart from the products it manufactures and can retain or reject—is in every cell tolerably similar to itself. The fundamental chemical resemblance of all protoplasms is certain, and thus we may speak of their typical composition. We may sum up the work of physiological chemistry for the last three quarters of a century by affirming that it has established the chemical unity of all living beings—that is to say, a very notable analogy in the composition of their protoplasm.

This living matter is essentially a mixture of the proteid or albuminoid substances, to which may be added other categories of immediate principles, such as carbohydrates and fatty matters. But the latter are of secondary importance. The essential element is the proteid substance. The most skilful chemists have tried for more than half a century to discover its composition. Only during the last few years—thanks to the researches of Kossel, the German chemist, following on those of Schultzenberger and Miescher—we are beginning to know the outer walls