36 ACTIVE IMMUNIZATION. 



It can be deduced from this experiment that i/ioo of a loopful of swine 

 pest, which represents i/io of a fatal dose for a guinea-pig by subcu- 

 taneous injection, can be converted into an acutely fatal dose by injecting 

 the aggressin simultaneously or a half hour before the experiment. 



The aggressin itself is only slightly toxic, and the quantity injected is 

 well borne by the guinea-pig. Its power of increasing the virulence of the 

 infective material varies directly with its quantity, i.e., the greater the dose 

 of aggressin, the more rapidly is death occasioned. If, however, only small 

 doses of the culture are given, and in addition to this, the aggressin is injected, 

 the animal does not die, but becomes exceedingly ill, thus indicating the 

 effect of aggressins. In this connection it might be well to add that the 

 aggressin may be given twenty-four hours previous to the time of infection. 



On microscopical examination of the aggressin exudate, of only very few 

 cells, but a great number of bacteria are present. The bacteria here have 

 increased during the short time after the infection to a far greater extent than 

 they would have done in an artificial medium. The body, continually 

 combatting against their increasing toxicity, finds itself powerless when 

 its limited fighting capacity, decreasing in proportion to the rise in strength 

 of the hostile micro-organisms, is expended, and ultimately succumbs to the 

 infection. During the struggle between the protective forces of the organ- 

 ism and the invading bacteria, many of the latter are destroyed and these 

 disintegrated bacteria are found within the exudate. . From this fact Wasser- 

 mann and Citron have formed the conclusion that the aggressins are not as 

 Bail claimed, secretory products of live bacteria produced during the con- 

 flict between the bacteria and the body organism, but rather the products of 

 broken down bacteria. Therefore, Bail's supposition that aggressins are 

 only obtained in the living body is erroneous and can be shown to be so by 

 the fact that aggressins may be reproduced whenever the essential require- 

 ments can be had, and these are : 



1. Large numbers of bacteria. 



2. Non-poisonous agents which can disintegrate these bacteria. 

 Aggressins thus obtained are known according to Wassermann and Cit- 

 ron, as "artificial" in contrast to Bail's "natural" ones. 



Wassermann and Citron Method of Obtaining Artificial Aggressins. 



Cultures are grown in mass on Kolle's flask plates. A Kolle's agar 

 plate is equivalent to twelve agar slants. For the inoculation of these 

 flasks a long platinum loop is needed which transfers some of the culture to 

 the plate. The transferred material is then spread over the entire surface 

 of the flask by a large triangular platinum loop. The latter is made by in- 

 serting into a holder both ends of a not too thin platinum wire, about 20 cm. 

 in length which is then shaped into a triangular form. While still red hot, 



