Standardization of the Peptone.—Let us assume that we have to deal with placenta peptone. This is mixed with the serum of individuals, who are certainly not pregnant, and then there should be no alteration of the original rotation. Should this not be the case, then the peptone is certainly not free from sulphuric acid or barium. With the serum of pregnant individuals a decomposition is bound to take place. At first, readings are taken every hour, and tests are made with many sera. A normal curve for the peptone is constructed, from the separate readings, by marking the angle of rotation on the abscissa and the time on the ordinate (cf. the curves given on pp. 62, 64, and 75-77). Once the normal alterations of rotation of the serum peptone mixture are known, then the readings for the diagnosis of normal cases need only be taken every four to six hours. If one has a special object in view, then the readings are taken more often.
The optical method supplements the dialysation process in many directions. In the first place, it is possible to determine quantitative differences in the speed of the decomposition. Further, qualitative differences may be observed. In the dialysation process, on the other hand, the dialysate may be used for experiments on animals and, for instance, be injected, in a state of concentration, for the purpose of deciding, whether certain
