PROPERTIES OF ANTISENSITIZERS. 303 



important detail. Imbued with the idea that the rabbit > ox 

 immune serum contains only a small amount of "y" suitable for 

 goat alexin, Ehrlich and Morgenroth think it indispensable to mix 

 with the given dose A of antiserum, as, in the first experiment, a 

 much larger amount of rabbit > ox immune serum than was used 

 in the first instance. They think this technic is justified because 

 even a large amount of the serum would contain only a small 

 amount of the "y" which is to be tested against the antiserum and 

 is alone of importance, since it is the only sensitizer that can hemo- 

 lyze the corpuscles in conjunction with goat alexin. They do not 

 consider that, in adding this excess of immune serum, they introduce, 

 not only a large amount of specific sensitizer, which is the only 

 substance they have in mind, but also a large amount of normal 

 sensitizers, which, as we know, monopolize a greater part of the anti- 

 sensitizing power and so prevent the specific sensitization from being 

 neutralized by the antiserum. Of course under these conditions 

 the corpuscles are hemolyzed. A small amount of normal serum 

 would have been just as effective in hiding the antisensitizing 

 effect as was the excess of immune serum. Under such conditions 

 no corpuscle protection would have been evident even if guinea- 

 pig alexin were used instead of goat alexin. Ehrlich and Morgen- 

 roth's laborious considerations on the nature of antisensitizers, 

 on the multiplicity of antibodies, and particularly on the multi- 

 plicity of sensitizers in a given immune serum lead to an incorrect 

 conception of the experimental results. It is evident from this 

 example that the logic employed in defending the lateral-chain 

 theory is far from unassailable; indeed, in certain instances it is 

 open to severe criticism and cannot be accepted without argument. 

 Theories of passive immunity. The immunity conferred by 

 injecting preventive serum presents certain peculiarities that have 

 recently attracted considerable attention. It was formerly thought 

 that the animal that received antitoxin and benefited from it 

 acted simply as a passive recipient without any reaction, or the 

 elaboration of any antagonistic substance even when the serum 

 injected was from an alien species. The fact that the duration 

 of passive immunity is brief was always supposed to be due to 

 a gradual elimination of the antibodies. This was the general 

 opinion, which we ourselves shared when we demonstrated in 1895 



