THE HiEMOFLAGELLATES. 



223 



ticular form, is added to blood containing it; in such a case agglomeration 

 is very rapid and frequently total — i. e. embracing the entire number of 

 individuals present. Laveran and Mesnil consider that this peculiar occur- 

 rence is intimately connected with the development, in the blood of the 

 host which is undergoing the immunisation, of a substance which has this 

 specific property towards that Trypanosome ; in other words, of a specific 

 agglomerine, perfectly analogous to the agglutinines that cause the 

 agglutination of Bacteria. Probably this specific agglomerine is present, 

 or can be produced, in a rat infected for the first time, but only to a very 

 slight degree ; with successive reinfections its power is greatly increased. 

 Moreover, sera other than that of the particular kind of host, for the time 



Fig. 19. 



Fig. 20. 



Fig. 19. — Binary union or agglomeration of T. hrucii. (After 

 Bradford and Plimmer.) 



Fig. 20. — a, ditto of T. lewisi; B, agglomeration cluster or 

 primary rosette of same parasite. (After L. and M.) 



being, of a given parasite, may also possess, in a varying degree, this 

 agglomerative property towards that Trypanosome ; in such cases, of course, 

 the agglomerine concerned is not specific. Lastly, agglomeration has also 

 been produced by the addition of chemical solutions, and in artificial 

 cultures of the parasites. For fuller details and examples of the compara- 



and immunising powers. Again, certain sera which exhibit the former 

 property towards a given Trypanosome may not be able to prevent infection 

 by that form. Laveran and Mesnil consider that the " preventivity " of a 

 serum is principally dependent ujion its enhanced phagocytic activity. 



