32 QUATERCENTENARY STUDIES IN PATHOLOGY 



of which showed no phagocytosis whatever. Animals which had not 

 attained this stage of hypersensibility either do not die at all, or only 

 after some days or weeks, and then with well-marked phagocytosis in the 

 exudate. He has shown that in the blood-serum of tuberculous animals 

 or tuberculous exudate there is a substance which he names " Aggressin," 

 which has the power of holding active phagocytosis in abeyance in 

 anrmals in which the tubercle bacillus is a true parasite ; and he has 

 been able by successive inoculations of these exudates to attain high 

 degrees of immunity. Hoke (^) has applied himself to the investigation 

 of the "aggressive" action of diplococcic exudates, and comes to very 

 remarkable and important conclusions. The rabbit is employed, 

 being an animal in which the pneumococcus is a true parasite.- 

 By intrapleural injection of cultures of pneumococcus isolated from a 

 lung abscess secondary to acute croupous pneumonia, a rabbit was killed 

 in 8 to 10 hours, and, post mortem, 20 cc. of exudate was obtained from 

 the pleural cavity. In this exudate numerous cocci were found, but no- 

 phagocytosis. The exudate was centrifugalised for 12 hours or longer,- 

 and all the cocci removed and subsequently carefully sterilised with 

 toluol. -By prolonged standing in the incubator the toluol separates and 

 forms a distinct layer, which can easily be pipetted off the top of the 

 serum. 



Should such a pneumococcal exudate possess " aggressive " properties, 

 it must be capable of shortening the duration of the disease, 

 because it holds in abeyance the natural protective power of the body, 

 and allows the bacteria to multiply rapidly, without being engulfed by 

 the phagocytes. Intrapleurally and intravenously were injected in one 

 series of rabbits fresh pneumococcus emulsions in quantities of 0'2 to 0*5 

 cc, along with a quantity (2 cc.) of exudate : into the control series, 

 instead of the exudate, normal saline was injected. The first series died 

 in every case earlier than the control. 



A remarkable property of ^' aggressive " exudates is that the aggressin 

 action can be inhibited by the addition of leucocytes. This was also 

 shown by Bail (^9) for cholera, and by Hoke (^) for staphylococcic 

 exudates, though first demonstrated by Kikuchi (^i). Aleuronat was 

 injected into the pleural cavity twelve hours before an injection of 

 aggressin, and pneumococcal emulsion, and in that case death was much 

 later than in the controls to which no aleuronat had been administered. 



(396) 



