MODE OF ACTION OF CYTOLYTIC SERA. 237 



us sufficiently proved by all these experiments.* We must now 

 take up certain objections that have been offered to this opinion, 

 some of which seem rather serious. 



Ehrlich and Morgenroth found that the serum of a goat immu- 

 nized against sheep blood, when heated to 56 degrees or even higher, 

 loses its power of destroying various species of corpuscles, such as 

 the guinea-pig and the rabbit, which it previously attacked. This 

 loss affects the non-specific hemolytic power present in normal 

 goat serum and acting on corpuscles not used in the immunization 

 of this animal. But this goat serum still shows a distinct ability 

 to destroy sheep blood, for which it is specific. Ehrlich and Mor- 

 genroth conclude that this serum contains several alexins, some 

 of which are destroyed at 56 degrees and others of which resist this 

 temperature. It is just as easy to imagine that we have to deal 

 with a single alexin modified or attentuated by heating. The 

 alteration is sufficient to inhibit the hemolysis of non-sensitized 

 corpuscles, which is never very strong, but does not prevent the 

 destruction of corpuscles that are sensitized and so rendered more 

 susceptible by the same serum. 



In another experiment Ehrlich and Morgenroth pass the serum 

 of a normal goat, that destroys guinea-pig and rabbit corpuscles, 

 through a Pukal filter. After filtration the serum still destroys 

 guinea-pig corpuscles, but does not affect rabbit corpuscles. Accord- 

 ing to these authors one of the alexins is retained by the filter and 

 the other passes through; this would imply that the two alexins in 

 question must have well-marked chemical differences to act so 

 differently in respect to the filter. It is to be noted that here again 

 we are dealing with hemolysis by a normal serum which is never 

 intense and may be affected by slight variations. It is quite evi- 

 dent that the serum after filtration does not have as much alexin 

 as before, but there is no reason for supposing that there are two 

 distinct alexins. It may well be imagined that filtration, by remov- 

 ing from serum some of its elements, has so modified its physical 

 properties as to render it less favorable for preserving corpus- 

 cles; we may well imagine, then, that certain species of corpuscles, 



* It is also in harmony with the fact we previously established, that an anti- 

 alexic serum, neutralizing the alexin of the serum of a given species, protects the 

 various cells that are affected by this alexin, even when they are sensitized. 



