CHAPTER VII 



IMMUNITY MECHANISMS IN EXPERIMENTAL 

 INFECTIONS 



The question of resistance to infection lias been studied experi- 

 mentally with considerable profit since Ashoff and Maximow 

 crystallized oiir present concept of the retieulo-endothelial system. 

 This chapter will be devoted to summarizing results and conclu- 

 sions of Gay, Cannon, Teale, Goodpasture and others who have 

 investigated the mechanism of resistance employed by the animal 

 body to localize infection or to free the blood stream of bacteria 

 and to favor recovery from infection. 



Experimental Streptococcus Infections in Rabbits. — Gay (1923, 

 1926) and his colleagues studied the defensive mechanism of the 

 pleural cavity of rabbits against experimentally produced infec- 

 tion with a highly virulent hemolytic streptococcus. They first 

 injected a sterile irritant (aleuronat) which caused an inflam- 

 matory reaction in the pleura with the formation of granulation 

 tissue. Polymorphonuclear leucocytes appeared in great numbers 

 early in the reaction. Later there was an increase in mononuclear 

 phagocytes both in the exudate and within the tissues. 



If virulent streptococci were introduced when the neutrophiles 

 predominated, the animals died as rapidly as the controls. If 

 they were injected after the mononuclear phagocytes were mo- 

 bilized, the animals could withstand many lethal doses of strepto- 

 cocci inoculated either into the pleural cavity on the side where 

 granulation tissue had been produced or into the opposite side 

 where none was present. In the latter case the protection was 

 due to clasmatocytes coming over as reinforcements from the depot 

 of mobilization in the opposite side. Gay and his associates speak 

 of this as "transpleural mohilization" of clasmatocytes. 



Linton (1928), working in Gay's laboratory, transplanted irri- 

 tated omentum (rich in clasmatocytes) into the peritoneal cavity 

 of normal rabbits and found that the rabbit's resistance to intra- 

 pleural infection with Streptococcus liemolyticus was greatly in- 

 creased. 



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