AGGRESSItfS 179 



of bacteriolysis with large amounts of immune serum, as follows : 

 When the amboceptors are in large excess, a portion combines 

 with the complement, leaving some amboceptors free, and these 

 free amboceptors then unite with the receptors before the activated 

 amboceptors (amboceptors + complement) do, and thus the comple- 

 ment -amboceptor groups are rendered inert. The reaction is 

 represented diagrammatically in Fig. 34. Arrhenius, however, does 

 not accept this explanation. He says : "If we have the compounds 

 ea and ab which may combine to form the compound eab, the 

 formation of the latter depends wholly upon whether e has a greater 

 affinity for ab than for a. If not, then eab is not formed, even if a 

 is not present in excess." (a = amboceptor, e = microbe, b = com- 

 plement.) The phenomenon may be quite analogous with the 

 inhibition met with in agglutination (p. 188). 



Aggressins 



Bail has discussed the question of the relationship between 

 bacteriolysis and immunity. He argues that there is apparently 

 little relationship between the bactericidal properties of the body 

 fluids and the immunity of an animal to infection through bacterio- 

 lytic processes ; and points out that in rabbits immunised against 

 anthrax there is no bacteriolytic power, the bacteria disappearing 

 gradually as the result of phagocytic action of cells, chiefly marrow- 

 cells ; that a comparison of the sera of sheep, rabbits, and cattle 

 shows great variation in their content of immune body, though the 

 animals are almost equally susceptible to anthrax ; and that in 

 test-tube experiments a bacteriolytic serum is blocked when the 

 conditions are approximated to those in the body by the addition 

 of body cells to the mixture ; the bactericidal properties of the 

 serum disappear or are greatly inhibited. Kruse suggested that for 

 infection to take place the invading bacteria must elaborate chemical 

 substances which so act on the cells and fluids of the invaded animal 

 that they overcome its natural resistance against infection. These 

 substances are considered by him and Bail to be distinct from the 

 toxins, and are termed by these writers " aggressins. " x The 

 aggressins are supposed to be secreted by the living uninjured 

 bacteria and not to be extracts, nor derived by solution, of the 

 bacteria ; they occur particularly in the fluids of pathological 



1 See Cenlr. f. Bakt., Orig., xlii, 1906, pp. 51, 139, 241, 335, 437, and 

 546. Also an excellent summary by Marshall, Philip'pine Journ, 

 of Science, vol. ii, 1907, p. 352> 



