them exclusively by the manner in which they act, and that is why, in must questions relating to ferments and their activity, we are only able to answer with conjectures. We may imagine that a ferment is directed against a simpler product of decomposition, and yet that it attacks at the same time a more complicated molecule, in so far as the group through which it attacks the substrate is actually present therein and within reach. It only depends on whether the ferment is able to find a group, corresponding to its own structure and configuration, in the particular molecule. We must, also, not forget that, in a body of high molecular structure, the same grouping may recur many times. In any case we consider it very possible that cases are met with in which the optical method shows a decomposition, while the dialysation process gives a negative result; although it must be admitted that, up to the present, not a single case of this kind has been satisfactorily proved.
All these discussions would be superfluous, if we only knew, on the one hand the nature of the ferments, and on the other the components that are out of harmony with the plasma. As it is, we are simply faced with the fact that ferments, directed against particular substrates, are to be found in the blood serum under very definite conditions. What is entirely new is the clear demonstration of the fact that the animal organism, within certain limits,
