AGGRESSINS 293 



The theory of Bail ' as eventually formulated, after extended in- 

 vestigations which need not be outlined, contains the following basic 

 principles :' 



Pathogenic bacteria differ fundamentally from non-pathogenic 

 bacteria in their power to overcome the protective mechanism of the 

 animal body, and to proliferate within it. They accomplish this by 

 virtue of definite substances given off by them, probably in the nature 

 of a secretion, which acts primarily by protecting them against phagocy- 

 tosis. These substances (referred tO by Kruse as " Lysins ") were named 

 by Bail, "Aggressins." The production of aggressins by pathogenic 

 germs is probably absent in test-tube cultures, or, at any rate, is 

 greatly depressed under such conditions, but is called forth in the animal 

 body by the onslaught of the germicidal or other influences encountered 

 after inoculation. 



These aggressins can be found, according to Bail, in the exudates 

 occurring about the site of inoculation in rapidly fatal infections. He 

 obtained them, separate from the bacteria themselves, by the prolonged 

 centrifugation and subsequent decanting of edema fluid, and pleural 

 and peritoneal exudates. 



Two fundamental experimental observations are brought forward 

 by Bail in support of the truth of his contentions. In the first place, he 

 was able to show that fatal infection could be produced in animals by 

 the injection of sublethal doses of bacteria, when, together with the 

 germs, there was administered a small quantity of "aggressin." He 

 inferred from this experiment that the injected aggressin had served in 

 paralyzing the onslaught of phagocytic and other protective agencies, 

 and had thus made it possible for the bacteria to gain a foothold and 

 to proliferate. 



The second experimental support upon which Bail's theory is 

 founded consists in the successful immunization of animals with aggres- 

 sin. Animals were treated with aggressive exudates, from which all bac- 

 teria had been removed by prolonged centrifugalization and which had 

 been rendered entirely sterile by three hours' heating to 60° C. and by the 

 addition of five-tenths per cent of phenol. Animals sa treated were not 

 only immune themselves, but contained a substance in their serum 

 which permitted the passive immunization of other untreated animals. 

 Bail explained this by assuming the production of antiaggressins in the 



> Bail, Arch. f. Hyg., lii, 1905; liii, 1905; Wien. klin. Woch., xvii, 1905. 

 "Bail und Weil, Wien. klin. Woch., ix, 1906; Cent. f. Bakt., I, xl, 1906; xhi, 

 1906. 



