Acquired immunity against micro-organisms 295 



merits as to the granular transformation of the vibrios. Thus, they 

 observed on several occasions that an extract of the spleen set up 

 this transformation in a particularly distinct and rapid fashion at 

 a period when the blood and serum, used in a much stronger dose, 

 were incapable of producing the same effect. Now, as Pfeiffer's 

 phenomenon is a visible manifestation of the action of the specific 

 fixative, it cannot be doubted that the spleen is really the principal 

 seat of development of the fixative substance before it makes its 

 appearance in the blood. 



Before concluding this chapter we must review very briefly the 

 principal phenomena associated with acquired immunity against 

 micro-organisms. The extracellular destruction of these parasites 

 takes place in the living animal under special conditions only, when 

 the phagocytes suffer a temporary injury (phagolysis) and allow their 

 microcy tases to escape. These latter by no means represent attributes 

 of the body fluids, as is even yet maintained by some writers. These 

 soluble ferments are connected with the phagocytes and represent the 

 ferments of intracellular digestion. The cytases undergo no modifi- 

 cation during the process of immunisation and correspond to those 

 which act in natural immunity. 



The agglutinative substance often present in the normal fluids 

 of the body becomes much more developed in those of immunised 

 animals. It is truly humoral, as it circulates in the plasmas and passes 

 into the fluid exudations and transudations. But the part played by [310] 

 it in immunity is very restricted. 



The protective and fixative properties, most often closely con- 

 nected with each other, are very markedly developed in an animal 

 enjoying acquired immunity. They may act upon the micro- 

 organisms which become permeated by the fixative substance, or 

 upon the infected animal by stimulating its defensive reaction, but 

 they are incapable of affecting the vitality or virulence of the micro- 

 organism. The two properties (protective and fixative) reside in the 

 fluids of the body, but they are functions of the cell products. The 

 elements of the phagocytic organs (spleen, bone-marrow, lymphatic 

 glands), or phagocytes, produce the specific protective and fixative 

 substances which pass thence into the plasmas. 



The phagocytic reaction is very general in acquired immunity. 

 The phagocytes which have a very imperfect antimicrobial function 

 or none at all, become, as the result of vaccination, much more 

 active. They exiiibit a very marked positive chemiotaxis and 



