50 LOUSE FEEDING EXPERIMENTS 



by the appearance of rickettsia in lice fed upon them at dif- 

 ferent days of the disease. The prime object of these experi- 

 ments was to ascertain what organism was constantly found in 

 lice nurtured upon typhus patients. So our louse boxes were 

 placed as often as possible upon patients in the first days of the 

 fever; the work of previous observers (Nicolle, 1920), (Pro- 

 wazeki, 1915-16), (da Rocha-Lima, 1919-21) had indicated 

 that the blood was most infectious during the first period of 

 the disease. Consequently, the boxes in the latter half of our 

 work were fed upon at least four different patients and fre- 

 quently upon eight patients. 



