AGGRESSINS 125 



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- 

 organism, an acute and fatal infection followed. Similar results were 

 secured with the bacilli of dysentery, chicken cholera, pneumonia, and 

 other diseases. 



Bail's Classification of Bacteria. Bail found that bacteria differed 

 in their power of forming aggressins; he therefore used this principle 

 in making a division of bacteria into three classes, according to their 

 disease-producing power, as dependent largely upon whether or not the 

 microorganism can produce an aggressin that is active against the pro- 

 tective forces of the host, particularly against opsonins and leukocytes. 



1. Saprophytes, or those bacteria that, when injected even in large 

 doses, do not produce any characteristic disease. 



2. True parasites, or those bacteria that, when injected even in the 

 smallest amounts, will produce disease and death. These are truly 

 virulent, and the number of bacteria increase so rapidly as to be demon- 

 strable in every drop of blood and in all the organs. Examples of true 

 parasites are the bacilli of anthrax and of chicken cholera, the tubercle 



