LICE AND DISEASE 397 



of eggs may be glued to a single hair, and often at some distance 

 from- the skin. The eggs hatch in six or seven days, and the young 

 become sexually mature in about 15 days. This species, even 

 under favorable conditions, will live apart from its host only 

 ten or 12 hours. The eggs are said not to develop except at 

 temperatures between 68 F. and 86 F., which are approxi- 

 mately the temperatures to which eggs attached to hairs beneath 

 the clothing would be exposed. 



Lice and Disease 



The role of lice in the spread of disease has long been sus- 

 pected in an indefinite and uncertain way. Only recently, and 

 at the cost of the lives of several great investigators, has the 

 whole portentous truth regarding the transmission by them of 

 typhus and relapsing fever (North African and European types) 

 been brought to light. Foremost among the investigators of 

 louse-borne diseases stands the name of Nicolle and his associates, 

 who in 1909 proved that typhus fever could be transmitted by 

 the body louse, and in 1913 that the Algerian type of relapsing 

 fever could be transmitted likewise. Two American investi- 

 gators, Ricketts and Wilder, working independently of the French 

 workers, proved in 1910 that the body louse was instrumental 

 in transmitting typhus (tarbardillo) in Mexico, and in 1912 

 Anderson and Goldberger showed that the head louse could also 

 transmit it. Opinions differ as to whether the infection can be 

 transmitted through the eggs to the lice of the succeeding genera- 

 tion. In 1918 an American commission under Dr. R. P. Strong, 

 and a British committee under Sir David Bruce and Major Byam, 

 working under field conditions on the war front in France, dem- 

 onstrated that trench fever is a louse borne disease. 



There is every reason to belive that typhus fever is normally 

 transmitted exclusively by lice. Wherever the hording together 

 of promiscuous crowds of people becomes necessary and when 

 scrupulous cleanliness, either of necessity or of choice, is not en- 

 forced, there the lice will thrive and sooner or later the dread 

 disease will break out. The organism which is believed to be 

 the cause of typhus fever, Rickettsia prowazeki, is discussed on 

 p. 186. Nicolle and his fellow workers have shown that lice which 

 are fed on infected patients do not become infective until the 

 eighth and usually the ninth or tenth day afterward. The same 



