fuel on the one hand, and certain constructive units on the other.
Many observations point to the fact that parenterally introduced substances, in so far as they can be modified, are utilized by the organism; that is, they serve as nourishment. The digestion, which would otherwise take place in the intestine and prevent the passage of disharmonious material into the body, is performed by the blood.
It is an open question from what source these ferments, which we are going to call defensive ferments, take their origin. Many facts accord with the suggestion that the leucocytes play a part in this connection (see also Lit. 23). They probably give off these ferments to the circulation. If so, we should then have in the blood plasma phenomena more or less analogous to those observed, for instance, by B. Friedrich Müller, during the dissolution of the fibrin that is excreted into the alveoli in cases of pneumonia. We see here numerous leucocytes penetrating into the solid exudate and dissolving it, after which an absorption of the products of decomposition begins, a kind of digestion taking place in the interior of the alveoli. Here also, as can be shown by special experiments, ferments can be demonstrated in the contents of the alveoli (in the expectorated sputum) and these ferments take their origin from the leucocytes. The old view, whereby the leucocytes take up
