180 A MANUAL OF BACTERIOLOGY 



oedemas and cxudates, and may be obtained from these by centri- 

 fugation and sterilisation at low temperatures. Bail believes 

 that the aggressins cannot be anti-complements, anti-immune 

 bodies, etc., but are substances heretofore unrecognised and the 

 active substances of the infection, and he considers that in order to 

 produce true immunity in disease anti-aggressin sera must be 

 prepared. The following are some of the properties of these sup- 

 posed aggressins : (1) Sterilised aggressin with a non-lethal dose of 

 the corresponding organism renders the latter fatal ; (2) aggressin 

 alone is only slowly toxic, producing a prolonged illness with 

 emaciation preceding death ; (3) inoculation of aggressin with 

 bacteriolytic serum into the peritoneal cavity suspends the action 

 of the latter ; (4) aggressin with bacteria blocks phagocytosis. 

 Bail believes that the aggressins promote infection by interfering 

 with the protective mechanism of the infected animal, particularly, 

 if not solely, by inhibiting phagocytosis. Upon the power to pro- 

 duce aggressin Bail has classified bacteria into (1) true parasites 

 which always produce aggressin, e.g. anthrax and chicken cholera ; 

 (2) half -parasites, the aggressin-producing power of which is variable, 

 e.g. typhoid, cholera, dysentery, and plague ; (3) saprophytes. The 

 virulence of an organism does not coincide with aggressivity, and 

 extremely virulent bacteria may be half -parasites. 



Bail's hypotheses have been much criticised, and Wassermann 

 and Citron believe that the supposed aggressins are derivatives of 

 the bacterial protoplasm which have the power of combining with 

 the specific protective substances of the animal and so inhibit 

 the action of the latter ; they are, in fact, endotoxins of feeble 

 toxicity. 



HAEMOLYSIS. 1 Some blood sera possess marked powers 

 of dissolving the red blood- corpuscles of another species, 

 and of setting free their contained hemoglobin (e.g. goat 

 serum dissolves rabbits' and guinea-pigs' corpuscles, and 

 ox and human sera usually dissolve sheep's corpuscles), 

 and if an animal be injected with the blood-corpuscles of 

 another species its blood-serum generally acquires the 

 property of dissolving the blood- corpuscles with which 



1 See Bulloch, Practitioner, December 1900, p. 672, and Trans. Path. 

 Soc. Lond., vol. Hi, Part 3, 1901, p. 208 ; Gruber, " Harben Lectures," 

 Journ. State Med., 1902, February, March, and April ; Ehrlich, Collected 

 Studies on Immunity ; Muir, Studies on Immunity. 



