an albumen, peptone, or polypeptide solution, having a known composition in regard to substrates, is added; a polariscope tube is filled with the mixture, and the rotation is quickly ascertained by means of a good polariscope. The tube is then placed in an incubator, and from time to time the angle of rotation is again noted. To avoid mistakes another tube is filled with the same quantity of plasma or serum, and normal salt solution is added in the same quantity as the substrate solution employed; this mixture is then observed in the polariscope under the same conditions as the former. Finally, another test, with the substrate solution alone, is arranged in the same way. It is further essential to add to the mixture a measured quantity of a phosphate mixture for the purpose of preventing the action of the ferment from being in anv wav influenced bv changes in the reaction of the mixture. To prevent cooling of the polariscope tube its jacket is filled with water at 37° C., or an incubator is used, which can be fitted to the polariscope (see below, the technique of the optical method). Decomposition of proteins or peptones could never be observed in these experiments, so long as the blood was taken from healthy, normally fed animals.
We now take the animal under observation, i.e., the animal whose plasma or serum we are investigating, and introduce selected substances directly
