510 STUDIES IN IMMUNITY. 



sis, in other words, we admit the unity of the alexin at least func- 

 tionally, if not chemically. In conclusion, then, I think that the 

 opinion which I expressed in 1895 on the mechanism of acquired 

 immunity in accordance with which the animal body would seem to 

 direct the same weapon, the same alexin against various foreign 

 cells, owing to the presence of a specific sensitizer, is gradually 

 receiving the united agreement of scientists. 



In so far as concerns the mode of fixation of alexin, the divergent 

 opinions of Ehrlich and Morgenroth, and myself, are well known. 

 According to these authors, the sensitizers have a complemento- 

 philic group. I have already previously mentioned my own 

 opinion; I think that avidity for alexin logically resembles agglu- 

 tination or sensitivity to the flocculating action of salts. Taken 

 alone, neither the bacteria, or at least the great majority of them, 

 nor the agglutinin is affected by salt, but the complex which they 

 form is agglutinable by this electrolyte. In the same way neither 

 the amboceptor nor the antigen in question has alone any manifest 

 affinity for the alexin, but they form by their union a complex 

 which can absorb alexin, in other words, which has particular 

 properties of adhesion. As a result, as I have already noted, there 

 is no fundamental difference between sensitizers and such other 

 antibodies as antitoxins. There is no such thing as an ambocep- 

 tor; all antibodies on the contrary are "uniceptors." There exist, 

 however, antigens which, by uniting with the suitable antibody, 

 give complexes which can adsorb alexin, whereas other antigens 

 have no such property. I do not think it is necessary for me to 

 return to the experiments that I have described in my articles which 

 show that there is no means of determining any direct affinity of 

 sensitizers for alexin in absence of the antigen, and consequently 

 there is no reason for admitting the existence of a complemento- 

 philic group.* Other experimenters have brought out similar facts 

 which lead to the same conclusions. Thus, according to Frouin and 

 Muir and Browning, on passing serum through certain filters it is 

 found that the sensitizers pass through whereas the alexin is retained. 



* This is true, not only as regards sensitizers that act on corpuscles or bacteria, 

 but also, as Gengou has shown, as regards those that affect albuminoid substances; 

 in this case also fixation of alexin takes place only when both the antibody and 

 the antigen are present. 



