IMMUNITY AND SUSCEPTIBILITY. 561 



constituent of the blood serum and other body fluids. It is undoubtedly 

 produced by the various body cells (leucocytes, et. al.) and during the 

 immunization of animals with certain antigens it is probably increased 

 only slightly, if any, in amount. The complement is supposed to be 

 composed of two groups also, one a haptophore with which it combines 

 with the amboceptor and another a zymophore which really produces the 

 lytic action after the haptophore has combined with the amboceptor. 

 On heating the complement the zymophore group is destroyed and a 

 complementoid produced. This substance is similar to a toxoid and will 

 combine with amboceptor, but no lysis will result. It is, however, the 

 amboceptor, or so-called immune body, that undergoes the decided in- 

 crease during the processes of immunization. It can be accurately 

 demonstrated that the amboceptor must combine with the cell in question 

 before the complement can combine. Cells, such as bacteria or ery- 

 throcytes, may be saturated with amboceptor and washed and when the 

 complement is added and combined, lysis takes place. The complement 

 will not combine with the cells under any circumstances unless ambo- 

 ceptor is present and has first combined with the cells. It is probable 

 in a given serum or body fluid, there are several complements which 

 may activate a Variety of amboceptors. However, it has been shown 

 that the same complement will activate a variety of amboceptors of 

 certain kinds. 



While the majority of lytic sera are thermolabile some have been noted 

 which are thermostable to a certain degree. Hamilton has described 

 such a serum resulting after immunizing animals to Bact. pseudodiph- 

 theria and Horton has noted thermostable substances in normal rat 

 serum which are lytic for Bact. anthracis. 



Various sera have been noted which possess amboceptors for certain 

 cells, but are not lytic because they do not possess the necessary comple- 

 ment. For example, the serum of the dog contains amboceptors for Bact. 

 anthracis but no complement. If in this instance a foreign complement 

 such as that in guinea-pig or rabbit serum is added there will be lysis of the 

 bacterial cells. 



Occasionally the absence of complement is of benefit to the animal 

 in question and may account for the seeming natural immunity. For 

 example, the venoms of the poisonous snakes are nothing more than 

 amboceptors and when these substances are injected into an animal body 

 such as a hog which possesses no required complement, no lysis of the 

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