PATHOGENICITY FOR EXPERIMENTAL ANIMALS 191 



receptive to pneumococcal infection, but it is seldom used in re- 

 searches on Pneumococcus. Lamar* and also Neufeld and Haen- 

 del* proved the great susceptibility of the rat to pneumococcal in- 

 fection. The subcutaneous injection of 10" 5 cubic centimeters of a 

 virulent strain caused septicemia which resulted two days later in 

 death of the animal. 



McDowell 878 studied the effect of high air temperatures, com- 

 bined with different degrees of humidity, on resistance of rats to 

 intraperitoneal inoculation of pneumococci. It appeared that after 

 an exposure for two weeks to a temperature of 83°F., with the hu- 

 midity varying from 44 to 72 per cent, rats exhibited greater re- 

 sistance than did rats kept at medium temperatures. High or low 

 humidity with temperatures between 65° and 72°F. were unfavor- 

 able to the survival of the test animals. However, when rats accus- 

 tomed to moderate temperatures (67° to 71°F.) were inoculated 

 intraperitoneally with Pneumococcus and then exposed to a higher 

 temperature (83°F.) there was a lowering of resistance. 



Rats, as well as mice, proved to be susceptible to pneumococcal 

 infection when the organisms in the form of pulverized, dried, in- 

 fected blood or spleens were insufflated into the trachea by Kramar 

 and Gyiire. 757 McDaniels 876 " 7 employed rats in an investigation of 

 the immunizing action of orally administered pneumococcal vac- 

 cines and found the species to be suitable for the purpose. 



THE MONKEY 



Monkeys in captivity are susceptible to spontaneous pneumo- 

 coccal disease. Blake and Cecil (1920) 128 reported that pneumonia 

 might occur in epidemic form, due to spread of infection from ani- 

 mal to animal, when conditions favoring close contact existed. The 

 disease in monkeys, according to the authors, was identical in its 

 clinical features, complications, and pathology, with lobar pneu- 

 monia experimentally produced in monkeys by the intratracheal 

 injection of Pneumococcus and with lobar pneumonia in man. Two 



* Quoted by Neufeld and Schnitzer. 



