STUDIES ON THE SERUM OF VACCINATED ANIMALS. 25 



Hankin's theory, although resembling the bactericidal theory of 

 body fluids, is not open to the objections that may be offered to the 

 latter. 



The two essential points in these doctrines are the following: 

 1. There is a bactericidal substance in solution in the body fluids, 

 and bacteria are taken up by the phagocytes only after having been 

 subjected to the influence of this substance. But, far from being 

 subsequent to a preparing action on the part of the bactericidal 

 substance, phagocytosis takes place with surprising rapidity; it 

 begins, indeed, immediately after inoculation of the organisms. In 

 the case of cholera particularly we have just seen that shortly after 

 the intravenous injection of cholera vibrios a number of them are 

 found inside of phagocytes. And, what is more, it has frequently 

 been proved by Metchnikoff that cells can take up living bacteria. 



2. Bactericidal substances are elaborated by eosinophilic leuco- 

 cytes. It is known, however, that these cells are of no great impor- 

 tance in defense of the organism. Phagocytosis and the destruction 

 of bacteria, moreover, goes on very well in invertebrates, although 

 they have no eosinophiles. As we shall see later on in our experi- 

 ments on "phagocytosis in vitro," various bacteria when mixed 

 with an exudate rich in phagocytes, but containing no true eosino- 

 philes, are rapidly taken up and modified in their form and staining 

 reaction. 



Denys * and his pupils think that leucocytes play an important 

 part in the elaboration of bactericidal substances; and they en- 

 deavor to reconcile the phagocytic and the humoral theories. 

 Buchner | is inclined to admit that leucocytes are of great impor- 

 tance in the formation of bactericidal substances. 



There are two phases to the problem; first: do the leucocytes 

 form the bactericidal substances found in serum? And, secondly: 

 if the leucocytes really form these bactericidal substances, do they 

 retain them during life or do they excrete them into the surrounding 

 plasma? 



It is perfectly evident that in order to draw conclusions from 

 experiments which are of any value to our knowledge of immunity, 

 we must study the bactericidal property in its simplest aspects and 



* La Cellule, 1893 et 1894. 



f Buchner, Munchener medicinische Wochenschrift, 1894. 



