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These exudates, after this treatment, showed exactly the same aggressin 
action as those which were produced by the occurrence of the infection 
in the living animal. Similar experiments were now performed with 
rabbits’ normal blood serum to which the bacteria were added (in vitro), 
the mixtures being further treated in the same way. These sera also 
showed properties similar to those of the aggressins. Finally, the bacteria 
were merely suspended in distilled water, thoroughly shaken, sterilized, 
and separated by centrifugalization from the fluid; the watery extracts 
which were thus obtained and which contained the soluble substances of 
the bacteria also possessed exactly the same action as did Bail’s aggressin 
exudates. Therefore, Wassermann and Citron conclude that the so-called 
aggressins of Bail have nothing to do with the living animal organism 
and that they are not new bodies but merely dissolved bacterial substances, 
with the immunizing properties of which we have long been familiar. 
Shortly after the appearance of his first paper, Bail and his pupils and 
associates published further articles demonstrating that high and un- 
doubted immunity could be obtained in animals by the inoculation of 
these so-called aggressin exudates. Bail demonstrated such results for 
typhoid, cholera, and anthrax infection, while Kikuchi '* showed that by 
the use of dysentery aggressin guinea pigs could be immunized against 
infection with dysentery bacilli and rabbits against the action of the 
dysentery toxin. Still more important were the results obtained by 
Weil’ in the immunization of animals against chicken cholera with 
aggressin exudates. he difficulties in obtaining active immunity against 
hemorrhagic septicemia have for a long time been well recognized. 
Inoculations with attenuated, living cultures have proved to be very 
unsatisfactory and Voges,’® using killed cultures, obtained unfavorable 
results. However, Kitt,"° who employed the cdematous fluids from 
animals dead of the affection, had better success. The production of a 
protective immune serum for this disease has also been difficult ; indeed, 
several observers have maintained that hitherto a method of obtaining 
such a satisfactory serum has not been known. However, with the 
exudates containing aggressin, collected from the pleural cavity of animals 
infected with chicken cholera bacilli, Weil was able to immunize other 
animals and to obtain a protective immune serum of high potency. He 
points out that the action of this serum is not bacteriolytic but that 
it possesses anti-aggressive properties. As intimated, Weil’s experiments 
* Kikuchi: Archiv fiir Hygiene (1905), 52, 378. Ibid. (1905), 54, 297. See 
also the articles of Von Hoke on “Aggressive wirkung von Pneumokokken und 
Staphylokokken Exsudat,” Wiener Klin. Wehnschr, (1905), 18, 348, and Ztschr. 
fiir Hygiene (1905), 50, 541, and of Salus “das Aggressin des Colibacterium,” 
Wiener Klin. Wehnschr. (1905), 18, 660. 
“Weil: Archiv. fiir Hygiene (1905), 52, 412. Ibid. (1905), 54, 149. 
* Voges: Ztsehr. fiir Hygiene (1896), 23, 149. 
* Kitt, Kolle, und Wassermann: Handbuch d. pathogenen Mikroorganismen 
(1904), 4, 969. ; 
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