FORMATION OF DEFENSIVE FERMENTS 57 



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 incu- 

 bator, 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 con- 

 ditions 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 



- o 



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 pep- 

 tones 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 investi- 

 gating, and introduce selected substances directly 



