AGGRESSINS 123 



disease, the resulting exudate being composed almost exclusively of 

 lymphocytes, Bail 1 has advanced the hypothesis that bacteria may 

 secrete aggressins, or substances that aim to protect the microorganism 

 by either neutralizing the action of opsonins or directly repelling the 

 body-cells and preventing phagocytosis. Bail found that if he removed a 

 tuberculous exudate, sterilized it, and injected it into healthy animals, 

 it had practically no effect. If tubercle bacilli were injected alone, 

 lesions would develop in the usual number of weeks; but if sterile 

 exudate and tubercle bacilli were injected together, death would follow 

 in about twenty-four hours, indicating that the exudate contained a 

 substance that acutely paralyzed the defensive forces of the animal, and 

 thus greatly increased the virulence of the bacilli. That this effect was 

 not the summation of endotoxins in the exudate plus living microorgan- 

 isms was shown by Bail, who found that when large quantities of exudate 

 alone were injected no untoward effects resulted, whereas the injection 

 of a small amount of exudate, plus a sublethal dose of bacteria, would 

 regularly produce acute infection and death. Bail therefore concluded 

 that the exudate contained a substance that allowed the bacilli to become 

 more aggressive, and for this reason he called this hypothetic substance 

 "aggressin." He assumes that in a tuberculous animal the tissues are 

 permeated with the aggressin, and that when fluid collects in the body- 

 cavities after the injection of tubercle bacilli, this fluid contains large 

 quantities of aggressin. This prevents migration and collection of 

 polynuclear leukocytes, but not of lymphocytes, and hence allows the 

 bacilli to develop rapidly, producing acute symptoms. On the other 

 hand, when tubercle bacilli are injected into the peritoneal cavity of 

 a healthy guinea-pig, polynuclear leukocytes which engulf the bacilli 

 are attracted, thus inhibiting their rapid development, there being no 

 aggressin to prevent phagocytosis. 



Similar results were obtained with other microorganisms. Bail 

 inoculated cholera and typhoid bacilli into the pleural and peritoneal 

 cavities of animals, and an acute local infection occurred. From the 

 exudates so produced he removed the bacteria by centrifugalization, 

 and completed the sterilization with antiseptics or with heat at 44 C. 

 The clear fluid obtained was found to possess but mild toxic properties, 

 and large amounts could be injected into animals of the same species 

 without producing any marked effects; when, however, it was injected 

 into an animal together with a sublethal dose of the particular micro- 



1 Wien. klin. Woch., 1905, 8, 14, 16, and 17; Berl. klin. Woch., 1905, 15; Zeit. 

 f. Hyg., 1905, vol. i, 3; Arch. f. Hyg., 1905, 52, 272, and 411. 



