BACTERIAL PROTEINS 127 



ria, aggressins may be their defensive agents. This belief is in keeping 

 with the hypothesis of Welch 1 and also of Walker 2 , according to which 

 it may be presumed that bacteria, as living cells, when so placed that 

 they are exposed to the defensive forces of their host, are, under favor- 

 able conditions stimulated to produce reciprocal antibodies for their 

 protection, and to generate them in increasing amounts as may be neces- 

 sary. 



Bail regards the aggressins as new substances; as already stated others 

 regard them as simple endotoxins; still others believe them to be free 

 bacterial receptors, and that these receptors may combine with bacterio- 

 lytic amboceptors, producing, as it were, a deflection of the amboceptors, 

 so that the bacteria themselves are not attacked, and thus continue to 

 proliferate. The action of aggressins is not dependent upon the toxicity 

 of the endotoxins, for the fluid containing them is devoid of toxic effects; 

 at most, therefore, if they are of the nature of receptors, they possess no 

 toxophorous portion. 



. Whatever aggressins may be, and we regard them as antibodies of 

 bacteria, just as bacterioiysins are antibodies of tissue-cells, they appear 

 to be especially directed against opsonins. neutralizing these, paralyzing 

 leukocytes, and thus inhibiting or entirely preventing phagocytosis. 



Anti-aggressins may be produced experimentally by gradually 

 immunizing animals with sterile exudates, and this immunity may be 

 transferred passively from one animal to the other by inoculation of its 

 immune serum. These anti-aggressins are quite specific, and neutralize 

 the aggressins in an exudate. 



BACTERIAL PROTEINS 



In practically all bacterial bodies, after removal of toxins and endo- 

 toxins, a certain proteid residue remains, which, when injected into 

 animals, is able to produce various grades of inflammatory reaction 

 leading to tissue necrosis and abscess formation. This substance was 

 first thoroughly studied by Buchner, who named it bacterial protein, and 

 regarded it as identical in all bacteria, and having no specific toxic action, 

 but characterized in general by its power of exerting a positive chemo- 

 tactic influence on leukocytes, and thereby favoring the formation of pus. 

 For example, in the development of an ordinary staphylococcus abscess 

 it is probable that the proteins of the cocci, aside from their toxins, aid 

 in producing tissue necrosis and in attracting leukocytes to the infected 

 area. Similarly, an extract of dead tubercle bacilli may produce a 

 'Brit. Med. Jour., 1902, 2, 1105. 2 Jour. of Path., 1902, 8, 34. 



