INFECTION AND IMMUNITY. 463 



tjr following upon vaccination against infection, was 

 due rather to an abstraction from the tissues, by the 

 organisms that were concerned in the primarv attack, 

 of a something that is necessary to the growth of the 

 infecting organism should it gain entrance to the body 

 at any subsequent time. This view is known as the 

 * ' exh a ustion hypothesis. ' ' 



As to the exhaustion hypothesis of Pasteur, there is, 

 as yet, no evidence whatever for its support. The work 

 of Bitter,^ which was undertaken with the view of de- 

 termining if, in the process of acquiring immunity, there 

 occurred this exhaustion from the tissues of material 

 necessary to the growth of bacteria that might gain 

 entrance to them at some later date, gave only negative 

 results. The flesh of animals in which immunity had 

 been produced contained all the elements necessary for 

 the growth and nutrition of the bacteria against which 

 the animals had been protected, just as did the flesh of 

 nou-vaccinated animals. 



lu 1884 Metchnikoff ^ published the first of a series 

 of observations upon the relation that is seen to exist 

 between certain of the mesodermal cells of lower ani- 

 mals and insoluble particles that may be present in the 

 tissues of these animals. The outcome of these inves- 

 tigations was the establishment of his well-known doc- 

 trine of phagocytosis, the principle of which is that the 

 wandering cells of the animal organism, the leucocytes, 

 })0ssess the property of taking up, rendering inert, and 

 digesting micro-organisms with which they may come 

 in contact in the tissues. Metchnikoff believed that 



■ Zeitschr. fur Hygiene, 1888, Bd. iv. 



» Arbeiten aus dem Zoulogiscbea Institat der nniversiUit Wien., 1884, Bd. v. 

 Fortschritte der Med., 1884, Bd. ii. 



