Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/74

 shown that many processes go on exactly in the same way, qualitatively, as if the cell were intact. But the principal life process, the oxidation to carbon dioxide and water, is not found. Even slight injuries to the cells are sufficient to annul this important process. In such a juice it may be said that only the preparative functions remain—all of them processes which we usually ascribe to ferments. If to the juice obtained in this manner a peptone containing very sparingly soluble amino-acids is added—as, for instance, tyrosin or cystin—or else a kind of peptone in the building up of which an amino-acid takes part—and this may be easily detected at the moment of decomposition by means of a colour reaction —then it is very easy to ascertain whether the juice contains any ferment that is capable of splitting the peptone in question. The precipitation of the respective amino-acids, or the appearance of the colour reaction, announces the presence of the decomposing agent.

Still more conclusive results are obtained if combinations of a known structure—for instance, polypeptides, in the building up of which the above-mentioned amino-acids take active part—be chosen for the experiment. Or one may follow the decomposition in a polariscope tube. A certain quantity of

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