128 LICE AND THEIR MENACE TO MAN 



These droppings are partly fluid when passed by 

 the lice, and may be supposed to enter the minute 

 punctures in the skin as they do the lesions caused 

 by scratching. The fact that men who do not 

 scratch themselves when bitten by infective lice 

 develop trench fever at widely varying intervals 

 of time from the day when such lice begin to feed 

 on them, is strong presumptive evidence that it 

 is not the act of biting which conveys the disease. 

 Such infections have been produced after periods 

 varying from sixteen to thirty-five days, whereas 

 when droppings are rubbed into the broken skin 

 the interval which elapses before the fever 

 manifests itself is remarkably constant and is 

 usually eight days. Even when dry these drop- 

 pings have by no means ceased to be a danger as 

 the disease germ continues to exist in them, and 

 only awaits a suitable opportunity to flourish in 

 another man. Droppings in this state may 

 remain in clothes or blankets for weeks or months 

 and be eventually rubbed or shaken into wounds 

 or scratches of one who has never known a louse. 

 We have ourselves kept droppings of lice for 

 four months and then produced trench fever by 

 introducing them into the skin of a healthy man, 

 which shows how truly infectious they are. And 

 skin wounds are not the only portals for this 

 poisonous dust, the delicate membrane of the 

 eye being an equally open door. Only allow 

 the fine particles to get blown upon the eyeball, 

 and trench fever may be the consequence as we 



