Facts bearing on acquired immunity 245 



tardation was slight and transient, and exhibited itself especially 

 in serums to which von Liugelsheim, following Denys, had added 

 leucocytes. 



Von Lingelsheim also noted a certain degree of agglutination 

 of the streptococcus by the serum of vaccinated animals, although 

 this was much more feeble than in the case of the cholera vibrio 

 or the typhoid bacillus, when agglutinated by their corresponding 

 serums. Speaking generally, he regarded the direct action of the 

 body fluids as insufficient to bring about the rapid destruction of 

 the streptococci in the vaccinated organism. "Since the action 

 of the bactericidal substances is limited in time, the streptococci 

 are able to adapt themselves to these substances and recover their 

 former energy. As the phenomena of extracellular solution, of such 

 a form as those observed under the influence of the cholera anti- 

 bodies, are absent in the case of the streptococcus and as, on the 

 other hand, a considerable ingestion of these organisms by the leuco- 

 cytes is observed we must seek in the activity of these cells 



a second important element of the defence of the animal organism " [' 258 1 

 (p. 78). 



To Salimbeni 1 , who has carried out in my laboratory an in- 

 vestigation on this subject, we are indebted for the most reliable 

 information on the phagocytic reaction in acquired immunity against 

 the streptococcus. He studied specially the phenomena in the sub- 

 cutaneous tissue of a horse, hypervaccinated against Marmorek's 

 streptococcus ; this animal received in all, at several injections, about 

 five litres of living culture. In spite of this refractory condition, 

 an oedema at the point of inoculation was soon produced ; in this 

 the micro-organisms remained free and the leucocytes were sparse. 

 But the cellular reaction, at first insignificant, developed with 

 great rapidity and many leucocytes, amongst which the macro- 

 phages were much the more numerous, were attracted. The phago- 

 cytosis was still delayed for some time, but it continued to increase 

 and 20 to 24 hours after the inoculation it was complete. As 

 soon as the phagocytosis was well established the oedema began 

 to disappear. In the thick exudation, containing a mass of leuco- 

 cytes, the macrophages are filled with a very large number of 

 streptococci packed together. These cocci develop inside the cells, 

 cause them to burst and again become free. A fresh arrival of 

 leucocytes, however, takes place, this time mainly niicrophages. 

 1 Ann. de I'Inst. Pasteur, Paris, 1898, t. xii, p. 192. 



