150 THE PRINCIPLES OF IMMUNOLOGY 



nomenon of cytolysis represents a general biological phenomenon ap- 

 plicable to vegetable cells, exemplified by bacteria, and also to a wide 

 variety of animal cells. In both kingdoms there is a marked species 

 specificity exhibiting, as do other immune processes, the phenomenon 

 of group reactions. In so far as bacteriolysis is concerned, inhibition 

 zones appear, apparently similar to the inhibition zones of precipitation 

 and agglutination. Two bodies interact to produce cytolysis, a ther- 

 mostable body, the amboceptor or sensitizer, which may be increased 

 by immunization, and a thermolabile body, the complement or alexin, 

 which does not react to immunization. The amboceptor appears to 

 act by preparing the antigenic cells for the lytic action of the com- 

 plement rather than by furnishing a two-armed link between cell and 

 complement. The reaction takes place more nearly according to the 

 physical chemical laws of colloidal reactions than the simpler laws of 

 reactions between inorganic chemicals. The protection afforded an 

 animal which possesses bacteriolytic immune bodies is obvious, and 

 the role these bodies play in natural and acquired immunity to disease 

 must be of great importance. 



