2O2 THE OPTICAL METHOD; 



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 easilv 

 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 transform- 

 ation of a colloid into a diffusible crystalloid. This 

 transformation is the result of a hydrolytic decom- 

 position. In the optical method we start, for purely 

 technical reasons, not with albumen, but with pep- 

 tone 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 



