caETHODS OF SERO-DIAGNOSIS. . 203 



at o° C ; whilst the alexin or, as they termed it, complement, was 

 only able to enter into the hemolytic action at a higher tempera- 

 ture, and that through the amboceptor — behaving as a link — the 

 complement acted on the cell. Bordet and others, however, main- 

 tain that the sensibilizing substance acts more in the nature of a 

 mordant on the cell, the combination thus formed showing a 

 marked affinity for alexin, the whole phenomenon probably being 

 explained as an adsorption of alexin molecules by the molecules 

 of the combination of antigen and sensibilizing substance. 

 Although we are still accumulating evidence as to the site of 

 origin of immune-bodies, and have some facts pointing to the 

 spleen, lymphatic glands, and bone marrow as being their possible 

 sources of formation, yet their production in general was ex- 

 plained by Ehrlich, according to his theory, by supposing that 

 the body cells were possessed of receptors of different types, and 

 that, in the case concerned, the receptor which, when cast off 

 from the cell, constituted the amboceptor, had two combining 

 affinities, one cytophile by which it combined with the cell under- 

 going cytolysis. and the other complementophile, by which it 

 entered into union with the complement. 



As to the source of alexin, it is held by Metchnikoff that it 

 is derived from the leucocytes, and he, who terms it cytase ( re- 

 garding its cytolytic actions as being similar to that of a ferment, 

 being aided in its ferment action by the immune body, which he 

 calls fixator), holds that there are two varieties of cytase, one a 

 macro-cytase, derived from large mononuclear leucocytes, acting 

 chiefly on animal cells ; and the other, a micro-cytasc, derived 

 from the polymorphonuclear leucocytes, acting especially on bac- 

 teria, and believes that these only escape into the blood fluid after 

 solution of the leucocyte or. as it is termed, phagolysis. 



But whilst Metchnikoff recognises only two forms of alexin 

 or cytase, Ehrlich is of the opinion that there are several varieties, 

 each having an affinity for particular varieties of cells, whilst 

 Bordet upholds the theory of the existence of only one form of 

 alexin in the blood, bringing forward as his argument the occur- 

 rence of the Bordet-Gengou phenomenon or " fixation of the 

 complement " reaction. 



Whilst the limitations imposed by time and the nature of 

 this paper do not allow of the experiments of the different 

 workers in support of their different theories being brought 

 forward, we shall see, later, how the Bordet-Gengou phenomenon 

 has come to assume great importance in sero-diagnosis. 



Agglutinins. — To these bodies we must now pay some atten- 

 tion. They were noted by Gruber and Durham in 1896 when 

 studying Pfeiffer s phenomenon, and they found that if the serum 

 of an animal immunized against the cholera vibrio was added to 

 a culture of this organism in bouillon, the effect was to produce 

 a sedimentation of the bacteria growing in the broth, the organ- 

 isms forming into small masses, which fell to the bottom of the 

 vessel, leaving the fluid, in which they had been previously 

 suspended, quite clear instead of possessing a turbid appearance. 



