180 STUDIES IN IMMUNITY. 



there are two distinct factors concerned in the effect of sera on cor- 

 puscles: First, the greater or lesser amount of active substances in 

 the serum and, secondly, the particular sensitivity of the corpuscles 

 in question to the substances in the serum employed. Corpuscles 

 may be very susceptible to the effect of the active substances of one 

 serum and much more refractory to those in another normal serum. 

 Although the agglutinins in different normal sera are similar in their 

 method of action they are not identical; there must be certain slight 

 differences of chemical constitution between them to explain the 

 diversity of their effect on a given kind of corpuscles. The same re- 

 marks apply also to the alexins from different animal species. The 

 corpuscles, too, of different species differ in constitution and each 

 variety has its particular way of reacting with a given alexin or a 

 given agglutinin. 



We have, moreover, offered in our memoir on the mechanism of 

 agglutination an experiment which indicates that a given normal 

 serum contains several different agglutinins. 



*** 



It is well to consider how great a resemblance there is between 

 substances with similar properties in different sera. For example, 

 we may compare the agglutinins of normal sera with those of im- 

 mune sera and the agglutinins and sensitizing substances for blood 

 corpuscles with the corresponding substances for bacteria. 



We have already frequently repeated that, in the matter of alexins, 

 normal sera do not differ from immune sera, whether antimicrobial 

 or antihematic. 



And, what is more, the alexins that affect corpuscles seem to be 

 quite identical with those that affect bacteria. Both the property 

 of changing red blood corpuscles and the power of producing a gran- 

 ular transformation of vibrios, are frequently met with among sera. 

 Vibrios, especially when sensitized by cholera serum, are readily 

 changed into granules when placed in contact with normal serum 

 from the rabbit, guinea-pig, goat, hen, dog, rat or pigeon; only a 

 slight difference in intensity of action is shown between these 

 different sera.* These sera lose their activity against bacteria when 



* We are dealing here, it may be stated, with those bactericidal effects which 

 depend on alexins and which do not occur with sera heated to 55 degrees. The 

 typical example of this activity is the granular transformation of vibrios. There 



