k 



Acquired immunity against micro-organisms 251 



fluids of the body are very greatly increased. With the discovery that 

 the bactericidal property was so highly developed in the serums of 

 animals that had been vaccinated against vibrios arose the belief in [264] 

 the acquisition of a new and purely humoral property. R. Pfeiflfer, 

 especially, insisted on the fundamental difference between the power 

 of the serum of immunised animals to transform the cholera vibrios 

 into granules and the corresponding property of normal serums. In 

 the first case Pfeiffer's phenomenon exhibited marked specificity ; 

 in the second, it was much more general. A normal serum trans- 

 forms into granules, indifferently, vibrios that are very distinct from 

 one another ; whilst the serum of an animal vaccinated against 

 a particular species or race of vibrios gives Pfeiffer's phenomenon 

 with this species or race only. Bordet's^ researches have defi- 

 nitely settled this question. This investigator has shown that 

 Pfeiffer's phenomenon is produced, with all the usual serums, by 

 means of the same substances, the cytases (alexine, or complement of 

 Ehrlich). But in the serum of vaccinated animals there is added 

 to these cytases the fixative (sensibilising substance of Bordet, 

 immunising body or amboceptor of Ehrlich) which exhibits specific 

 properties. Having thus carefully distinguished the two substances 

 that set up the granular change in vibrios, Bordet shows that in 

 vaccinated animals it is the fixative which increases in quantity, 

 whilst the cytase remains pretty much in the same proportions as in 

 the normal animal. He demonstrated, in fact, that when we take 

 a very small dose of the serum of a vaccinated animal which by itself 

 is incapable of transforming the vibrios into granules, about the same 

 quantity of immunised serum or of normal serum must be added 

 to it in order that Pfeifffer's phenomenon may appear. The quantity 

 of cytase, that soluble ferment which is necessary for the production 

 of the phenomenon, is, therefore, about the same in the serum of 

 a normal animal as in that of a well-vaccinated animal. Whilst the 

 cytase does not increase as a result of vaccinal injections, the fixative, 

 on the other hand, becomes more and more abundant. Consequently 

 it is this second soluble ferment that impresses its characters on the 

 blood serum and on some of the other fluids of the vaccinated animal. 

 It has been pointed out in the preceding chapter that the fixative is 

 found in the fluid of the oedema of vaccinated animals, although in 

 less quantity than in their blood serum. It has also been mentioned 

 that no fixative is found in the aqueous humour of well-vaccinated [265] 

 ^ Ann. de VInst. Pasteur, Paris, 1895, t. ix, p. 462. 



