214 A MAMJAL OF BACTERIOLOGY 



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 supposed 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 produce 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. By " haemolysis " is meant the solution 

 of red blood-corpuscles and the setting free of their 

 contained haemoglobin. Many reagents possess this 

 property of dissolving red corpuscles, such as distilled 

 water, dilute acids, some bacterial toxins and snake 

 venoms and saponin. Some blood sera when fresh also 

 possess a similar power of dissolving the red corpuscles 

 of another species, for example, goat serum " hsemolyses " 

 rabbit and guinea-pig corpuscles, and ox and human sera 

 usually hsemolyse sheep corpuscles. The solvent sub- 

 stances causing hsemolysis are known as " hsemolysins." 

 The hsemolysin content of a naturally haemolytic serum 

 is usually small, so that if the serum be diluted five or six 



