Immunity against micro-organisms 313 



later, Denys 1 , in collaboration with Marchand, published another 

 memoir in which he describes experiments on the mechanism of the 

 immunity conferred on rabbits by injections of the blood-serum of 

 vaccinated horses. From these experiments they draw the conclusion 

 that "the serum of the horse immunised against the streptococcus 

 possesses no bactericidal properties, properly so called, against this 

 micro-organism ; it does not affect it directly ; but it contains a 

 substance which renders the phagocytic power of the leucocytes 

 extremely active. Even in the presence of small quantities of this 

 serum, the white corpuscles rapidly ingest the streptococci and are 

 capable of stopping all development so long as they retain their 

 amoeboid movements." "The action of the serum upon the leuco- 

 cyte in its conflict with the streptococcus, is really derived from the 

 horse immunised against this organism. It exists neither in the [329] 

 ordinary horse nor in the horse vaccinated against diphtheria" 

 (p. 15). Against these experiments of Denys and Marchand we 

 might bring the same objection that we raised against the analogous 

 experiments of Denys and Leclef, because, in both cases, these 

 writers lay too much stress on the presence or absence of the phe- 

 nomena of phagocytosis in preparations kept outside the body of the 

 animal. Under these conditions phagocytosis is effected in a fashion 

 too artificial to be capable of furnishing exact information. 



Von Lingelsheim 2 met Denys and Marchand with the fact that, 

 in their researches, the serum of the horse immunised against 

 the streptococcus was only feebly bactericidal. After a prolonged 

 contact (612 hours) with a specific serum, the streptococci, when 

 transferred to rabbit's blood, showed retarded development as com- 

 pared with streptococci subjected to the influence of the anti- 

 diphtheritic and antitetanic horse serum. Von Lingelsheim himself, 

 however, points out that the bactericidal action of the antistrepto- 

 coccic serum was feeble and transient, and required the intervention 

 of the reaction of the animal cells within the body. 



The researches carried out by Bordet 3 in my laboratory are not 

 open to the objections that we were justified in putting forward 

 against the experiments made by Denys and Marchand, since he care- 

 fully watched the phenomena of immunity as they developed in the 



1 Bull. Acad. roy. de med, de Belg., Bruxelles, 1896. 



2 Habilitations-Schrift, Marburg, 1899, and in von Behriug's "Beitrage 

 experimentellen Therapie," 1899, Bd. i, S. 40. 



3 Ann. de Vlnst. Pasteur, Paris, 1897, t. xi, p. 177. 



