gave good results, but the risk of infection is great. In any case, organs prepared in this way have also to be tested each time before use. The boiling process has this advantage over the other, that the tissues are loosened, and in this way are more easily acted upon by the ferment.
II. The Optical Method.
The principle of the Method.—The optical method enables us to demonstrate alterations in optically active substrates by a determination, with the aid of a polariscope, of changes in their angle of rotation.
The aim of the optical method is, in principle, exactly the same as that of the dialysation process. In the latter we determine the transformation of a colloid into a diffusible crystalloid. This transformation is the result of a hydrolytic decomposition. In the optical method we start, for purely technical reasons, not with albumen, but with peptone produced from the latter. We cannot use albumen, because it would prevent us determining the angle of deviation of the substrate-serum mixture. It would either give rise to precipitates, or else render the mixture so heterogeneous, that slight changes of rotation would be very difficult to follow. When using the optical method, we allow the decomposition, produced by the ferments present in the serum, to set
