150 TYPHUS IN GUINEA-PIGS 



TABLE XIII 



Number of Guinea-pigs 



Subcutaneous Intraperitoneal 



Days Inoculation Inoculation 



4 1 \ Secondary infection 



5 2 j suspected because of 

 600 high and prolonged 



7 1 13 temperature 



8 1 26 



9 4 40 



10 6 58 



11 1 29 



12 8 12 



13 6 12 



14 2 5 



15 3 3 



16 2 



17 2 



18 1 



19 1 

 35 204 



The three instances of incubation periods of less than seven 

 days, since they occurred only in guinea-pigs inoculated intra- 

 peritoneally and were followed by an unusually long course 

 of fever with unusually high temperatures, may safely be re- 

 garded as occasioned by the presence of a complicating in- 

 fection. 



Our conclusions in regard to the incubation period of typhus 

 in guinea-pigs irrespective of the source of virus, i.e., from the 

 louse, man or passage virus, are: 



1. That the minimum incubation period of the uncontami- 

 nated virus is seven days. 



2. That the repeated passage through guinea-pigs influences 

 (shortens) the incubation slightly as compared with the first 

 incubation period when inoculations are made from man to 

 guinea-pigs, but has no further effect after the first few trans- 

 fers. 



3. That the 92 per cent of the guinea-pigs inoculated by us 

 in maintaining the virus reacted between the seventh to 

 thirteenth days inclusive. 



4. That subcutaneous inoculations prolong slightly the 

 incubation period. 



