44 OFFENSIVE FORCES OF THE INVADING MICROORGANISM 



(a) that they are formed only in the living body of the host, (6) that 

 they are not toxic, and (c) that the immunity which results on injec- 

 tion with aggressin exudates is of a type that is definitely different 

 from the forms which were known before, viz., the antitoxic and the 

 bacteriolytic type. 



"Artificial" Aggressins. A careful investigation of Bail's work 

 has shown that these suppositions were, after all, not well founded. 

 Wassermann and Citron have thus demonstrated that substances 

 with the identical properties of the aggressins of Bail can also be 

 obtained in the test-tube by shaking cultures of various organisms 

 (the swine plague and hog cholera bacillus, for example) with dis- 

 tilled water, proving that the cooperation of the living organism of 

 the host is not essential. The products thus obtained, in contra- 

 distinction to Bail's "natural" aggressins, have been termed "artifi- 

 cial" aggressins; there is no real difference between the two, however; 

 the quantity is smaller, but with the one as with the other it is pos- 

 sible to transform subfatal doses of bacilli into fatal ones and to 

 bring about a certain type of immunity. The second assumption 

 of Bail that aggressin exudates are non-toxic has also been shown 

 to be incorrect, as the intraperitoneal injection of sufficiently large 

 amounts of dysentery, cholera, and staphylococcus aggressins, in 

 guinea-pigs, will not only cause general marasmus, but actually 

 lead to the death of the animal. 



In fine, it has been proved (by the precipitin test, which see) that 

 aggressin exudates contain bacillary proteins, all of which possess a 

 certain degree of toxic action, and cause the formation of certain 

 antagonistic substances when injected into animals. In the light of 

 such knowledge it is now possible to account in a more natural way 

 for those observations of Bail which led him to assume the existence 

 of aggressins as substances sui generis. The facilitation of infection 

 is thus readily explained by the fact that the injection of the sub- 

 fatal dose is accompanied by the simultaneous administration of a 

 certain amount of toxic material, and not of a non-toxic substance, 

 as Bail supposed, so that death is due to the two factors directly and 

 not to the one indirectly. This, however, was nothing new in itself, 

 since Bouchard already had shown that the filtrates of various 

 bacterial cultures facilitated bacterial infection (substances favori- 

 santes). More recently Doerr also could prove that both killed 

 cultures of various bacteria and bacterial toxins as such (diphtheria 



