IMMUNIZING EXPERIMENTS WITH ERYTHROCYTES. 159 



could passively reappear in the serum of the injected animal and so 

 simulate an active new formation of immune body. In accordance 

 with this the experiments were made as follows : Ox blood was treated 

 with an excess of inactive serum from a rabbit which had been im- 

 munized with ox blood, the mixture digested at 37-40 C. for half 

 an hour and then centrifuged. The decanted fluid was then tested 

 for its content of immune body. Only when this test proved posi- 

 tive, and it could therefore be assumed that all receptors had been 

 saturated, was the blood so treated employed for injections. But 

 it was previously repeatedly washed with physiological salt solution 

 in order to remove all free immune body. Finally the centrifuged 

 sediment was made up to its original volume. The course of such an 

 experiment is illustrated in the following: 



100 cc. ox blood are mixed with 25 cc. inactive immune serum 

 of a rabbit which has been immunized with ox blood. Of this im- 

 mune serum, 0.0025 cc. suffice, when complement is added, to just 

 completely dissolve 1 cc. 5% ox blood; the amount employed, there- 

 fore, represents five times the amount necessary to dissolve the 

 100 cc. ox blood. After the mixture has remained in the thermostat 

 for half an hour it is filled up to 300 cc. with 0.85% salt solution and 

 centrifuged. The first decantation is tested by adding it in decreas- 

 ing quantities to 1 cc. 5% ox blood plus 0.4 cc. normal rabbit serum 

 (as complement). 



The following results are obtained : 



1st. Decantation: 1.5 cc. complete haemolysis. 



1.0 cc. almost complete haemolysis. 



0.5 cc. " 



0.25 strong haemolysis. 



0.1 no 



From this it must be concluded that the blood-cell receptors are 

 incapable of further absorption; in other words, that they have been 

 saturated. 



The second decantation tested in this same manner yields the 

 following result : 



2d. Decantation: 3.0 cc. strong. 



2.0 " moderate. 

 1.0 " little. 

 0.5 " trace. 



It therefore contains only very little immune body. 



