220 IMMUNITY OF BACTERIA TO AGGLUTININS 



The subject has been investigated by others, and their results 

 do not altogether corroborate those of Walker. Thus Miiller 

 found the same inagglutinability after culture in diluted typhoid 

 serum, but did not find any evidence of the formation of an anti- 

 agglutinin ; on the contrary, he found that bacilli thus treated 

 had less power of weakening the action of typhoid serum than 

 had normal bacilli. We might explain his results by saying 

 the bacilli had lost their agglutinable receptors, or agglutinogen. 

 Bail, working with a different method, obtained comparable 

 results, though he explained them quite differently. He, as well 

 as Landsteiner and others, noticed that bacilli grown in the 

 immune serum grew into long branching threads, losing their 

 bacillary character entirely. This has been thought to be a sort 

 of end-to-end agglutination. 



The change is a more or less permanent one. Thus Park and 

 Collins found that cultures (of B. coli and B. dysenteric) which 

 had lost their power to agglutinate might require to be grown for 

 months on ordinary agar before they retained their normal sensi- 

 tiveness. The change is evidently a very profound one, and one 

 that is handed on for many generations. 



The subject has recently been carefully investigated by Marshall 

 and Knox, working with B. dysenteric. They found the same loss 

 of agglutinability when the bacillus was grown on immune sera, 

 but the same change also occurred when normal horse serum was 

 used ; and they further showed that the alteration was a rapid 

 rather than a gradual one, as Walker had found in the case of 

 B. typhosus. With regard to the mechanism of the process, they 

 proved conclusively that the modified bacilli had no power of 

 uniting with the agglutinin, as Miiller had also found. It is quite 

 clear, therefore, that the loss of agglutinability is due to the loss 

 of appropriate receptors, in this case at least. They point out, 

 apropos of Welch's hypothesis of toxins, that a bacterium which 

 attempted to protect itself against its host by the formation of 

 antibodies would have but a poor chance of surviving, whereas 

 by the simple process of losing some of its receptors they can 

 nullify some of the protective mechanisms possessed by the latter. 



Their explanation of the process by which these resistant 

 bacilli are produced is interesting and suggestive. They do not 

 think, with Walker, that the bacilli acquire a new character 

 i.e., the power of producing antibodies and transmit it to their 

 descendants, but that there is simply a process of natural selection. 



