234 STUDIES IN IMMUNITY. 



one kind of corpuscle prevents destruction of the second kind. 

 Controls show that the amount of either species of corpuscles added 

 is rapidly destroyed with even half the amount of each mixture 

 provided that the other kind of corpuscles has not previously been 

 added. 



The experiments reported in collaboration with Dr. Gengou in 

 the previous article are also of significance in this connection. They 

 prove that the addition to alexic serum of a sensitizer active against 

 bacteria does not deprive the serum of its power to destroy sub- 

 sequently added sensitized corpuscles or sensitized bacteria of 

 another Variety. But if the sensitizer added in the first place is 

 accompanied by the bacteria for which it is specific, the serum is 

 entirely deprived of its alexic power. Here again it is the sensi- 

 tizer plus bacterium and not the sensitizer alone that takes up 

 the alexin. 



We may now consider an objection that Ehrlich and Morgenroth 

 have raised to our hypothesis. These investigators imagine that 

 to agree with our conception a sensitized corpuscle should be equally 

 affected by any alexin coming from any animal species. They 

 mention the fact that rabbit corpuscles must be much more power- 

 fully sensitized to be hemolyzed by rabbit alexin than when guinea- 

 pig alexin is employed. 



The fact is exact; we are all the more ready to admit it as we 

 ourselves mentioned it in the article that gave rise to Ehrlich and 

 Morgenroth's objection.* We are at a loss, however, to understand 

 how these investigators should imagine that in our opinion sen- 

 sitized corpuscles should be equally susceptible to various alexins. 

 Our idea is quite the opposite. Since the alexins in the different 

 animal species are not identical, it is quite obvious that they should 

 not all have an equal tendency to destroy a given corpuscle. And 

 consequently a weak sensitization may at times render a corpuscle 

 susceptible to certain alexins, while a strong sensitization would be 

 necessary to cause weaker alexins to produce as great an effect. 

 In the instance under consideration, it is quite conceivable that 

 rabbit corpuscles must be strongly sensitized to yield to rabbit alexin. 

 which, under normal conditions, is quite harmless for its proper 

 corpuscles. It is evident, then, that a given dose of a given sensi- 



* See p. 187. 



