BACTERIAL INVASION 225 



As shown early in the text, excessive heat applied 

 to the splanchnic area results in varying degrees of 

 shock which, as we have seen, is due to the liberation 

 of cytost from the tissues. The increased resistance 

 to infection which was observed in the animals so 

 treated must have been due to the cytost released into 

 the circulation by the thermal injury of the splanch- 

 nic tissues. In this respect then, these early experi- 

 ments of the writer are in harmony with the more 

 recent findings of Bresredka cited above. Indeed, as 

 one examines the recent writings of prominent im- 

 munologists, one becomes impressed by the fact that 

 the experts in this field are beginning to realize that 

 cellular products liberated as a result of tissue damage 

 are of paramount importance in the development of 

 immunity, both specific and non-specific. In this con- 

 nection, the reader will find much of interest in the 

 reviews of Manwaring (1930), Zinsser (1931), and 

 Irons (1931). 



The localized formation of cytost due to the action 

 of bacteria in the tissues of a higher animal may lead 

 to the operation of other defense mechanisms. As is 

 well known, when a local infection resulting in abscess 

 formation takes place, a migration of phagocytes to 

 the site of infection occurs, and the body attempts to 

 protect itself against a generalized infection by wall- 

 ing off the infected tissues by the development of a 

 barrier of connective tissue. 



The importance of both these types of defense 

 mechanism has been recognized for a long time, but 

 the manner in which they are brought into play is 

 obscure. The migration of leucocytes to a site of in- 

 fection is usually classed as a chemotactic response, 



