296 STUDIES IN IMMUNITY. 



sitization. Under these conditions the antiserum is unable to 

 prevent hemolysis. 



Let us add 0.6 of a cubic centimeter of antiserum, which is a 

 large dose, to 0.2 of a cubic centimeter of sensitized ox blood. We 

 fill the tube with salt solution, centrifugalize, and remove the super- 

 natant fluid. To the sediment we add 0.6 of a cubic centimeter of 

 normal guinea-pig serum, 56 degrees, and 0.2 of a cubic centimeter of 

 guinea-pig alexin. Under these conditions no hemolysis occurs. 

 The experiment is repeated, with the variation of adding 0.6 of a 

 cubic centimeter of normal salt solution in place of the heated 

 guinea-pig serum after washing and then adding the alexin (0.2 

 c.c.). Hemolysis occurs completely in about an hour.* The cure 

 of the corpuscles, then, was only partial and the sensitization, al- 

 though weakened, is evident when the corpuscles are placed in a 

 medium that lowers their resistance.! 



Are we not justified in comparing this fact with the one noted 

 some time ago by Roux and Vaillard, namely, that a mixture of 

 tetanus toxin and antitoxin that is harmless for normal guinea-pigs 

 is dangerous for guinea-pigs that have been weakened by vacci- 

 nation with the cholera vibrio? 



Without considering these questions further for the moment, 

 we may return to the subject properly under consideration. 



Ehrlich's theory. Relates to the origin of antibodies and is as 

 follows: on injecting an animal with a substance that gives rise to 

 an antibody, the substance injected unites with certain chemical 

 elements (receptors) in certain definite cells. These cells are dis- 

 turbed and react. In reestablishing their previous condition they 

 form new receptors which, being produced in excess, are forced out 

 of the cell into the surrounding fluids and constitute the anti- 

 bodies. 



The theory offers, then, an easy means for determining the nature 

 of antibodies. Let us apply it to the antisensitizer we have been 

 studying. When guinea-pigs are immunized against rabbit serum 

 we must conceive of them as having, according to the theory, 



* A control shows that the same corpuscles without sensitization are unaffected. 

 We know, furthermore, that heated normal guinea-pig serum has no antisensitiz- 

 ing effect. 



f It is a well-known fact that salt solution renders corpuscles less resistant to 

 traces of hemolytic serum. 



