456 BIOLOGY OF PNEUMOCOCCUS 



alteration in susceptibility to pneumococcal infection by intra- 

 peritoneal inoculation. Similarly, animals desensitized by repeated 

 intracutaneous injection after the appearance of allergy ex- 

 hibited an unaltered susceptibility to infection. 



In 1927, Zinsser and Grinnell 1581 investigated the action in the 

 skin of normal guinea pigs of various bacterial autolysates in- 

 cluding those prepared from pneumococci. Reactions were noted 

 only in the case of well-grown animals, whereas young guinea pigs 

 almost invariably gave a negative reaction on the first test. On 

 further study it was found that the cutaneous reactions were 

 manifestations of hypersensitiveness which could be elicited by 

 bile solutions of Pneumococcus as well as by similar autolysates. 

 Sensitization could be induced by the previous injection of dead, 

 intact bacteria, as well as of autolysates, but the actual skin re- 

 action was elicited only by autolysates. When properly treated, 

 insensitive animals could be rendered sensitive within a space of 

 five to seven days by the daily injection of autolysate. The sensi- 

 tivity thus produced was related to the bacterial species and not 

 to pneumococcal type. Using the rabbit, Julianelle (1930), 689 

 after subjecting the animals to repeated intracutaneous injections 

 of heat-killed pneumococci, demonstrated increased skin activity 

 which reached a maximum after four to six injections had been 

 given and then diminished. After regression of the reaction to the 

 first injection of antigen into the skin, there frequently followed 

 a recrudescence or exacerbation of the reaction. By injecting the 

 serum of a highly reactive animal into a normal rabbit, the author 

 was unable to confer the property of skin-reactivity upon the re- 

 cipient. 



In another paper, Julianelle 690 communicated further results ob- 

 tained in rabbits during a study of actively induced skin-sensi- 

 tivity to derivatives of Pneumococcus. Positive reactions were 

 evoked in animals that had previously received repeated intra- 

 cutaneous injections of heat-killed pneumococci, of the pneumo- 

 coccal nucleoprotein, and of a solution of the bacterial cell from 



