SUMMARY OF THE EXPERIMENTS 109 



3. SUMMARY OF THE EXPERIMENTS TO PROVE THE SPECIFICITY 



OF RlCKETTSIA PROWAZEK1 FOR TYPHUS 



These experiments are reviewed in Table IX. 



In four of the boxes used for these experiments, Nos. xvii, 

 xvin, xix, and xxxvm, lice containing Rickettsia pr&wazeki 

 were found. In six of the boxes, Nos. xxi, xxn, xxvm, xxxiv, 

 xxxvi, and xxxvn, no lice were found to contain rickettsia. 



1. From the four positive boxes, each of the nine lice in 

 which rickettsia were found produced typhus in guinea-pigs. 

 The existence of typhus was proved in every instance but one 

 (louse W 241, guinea-pig 22) by adequate controls. 



2. From the four positive boxes, there were four lice in 

 which no rickettsia were found; but they produced typhus in 

 guinea-pigs. In each instance the existence of typhus was 

 proved by adequate controls. The failure to find rickettsia 

 in smears of such small amounts as were reserved for examina- 

 tion in these inoculation experiments does not prove their 

 absence from the lice; for, in the examination of serial sections 

 of entire lice from positive boxes, we occasionally have found 

 rickettsia in but a single cell. 



3. From the four positive boxes, there were seven lice in 

 which no rickettsia were found; they failed to produce typhus 

 in guinea-pigs. The failures were proved by adequate con- 

 trols in every instance but one (louse W 240, Box xvii); this 

 animal lived for forty days without evidence of typhus. 



4. One injection from a negative louse from a positive box 

 (louse W 223, Box xvin, guinea-pig 24) yielded inconclusive 

 results in that the guinea-pig, after a period of temperature, 

 died on the thirteenth day of pneumonia. 



5. From the negative boxes, no louse produced typhus in a 

 guinea-pig. Of the total of twenty guinea-pigs injected with 

 lice viscera from these boxes, the results were adequately con- 

 trolled in twelve, and not controlled in one instance (louse 

 W 240, Box xvii, guinea-pig 21) in which case, however, the 

 guinea-pig lived for forty days without evidence of typhus. 

 Three experiments were failures owing to the premature death 



