THE LIFE HISTORY OF HUMAN LICE SOJ 



are preferred. However, in case of necessity, the lice can and will oviposil 

 on smooth materials such as silk and sateen. It has been suggested thai 

 infestation could be greatly reduced and even remedied entirely by wear 

 ing for one to twenty -four hours a broad band of felt or rough wool undei 

 the clothes, with the idea that lice would collect on this, and they anc 

 their eggs could then be destroyed by burning. But the preference oi 

 lice for such material and the difference between this and the uniform is 

 not marked enough to make it really effective. 



In practical control work the question is likely to arise as to hoii 

 long discarded but untreated clothing will remain infective. The an 

 swer to this, of course, depends on how long lice can live without fooc 

 and how long it takes for all the eggs to hatch. Experiments shofl 

 that lice can live without food from two to three days at 35° C, thre« 

 days at 30° C, three to five days at 22° C, and about seven days a1 

 10° C. The lice cannot live long without food unless at ineffective tem- 

 peratures, the longest period recorded being ten days at 5° C 

 (41° F.). The longest record of fed adults is 46 days for a femalt 

 recorded by Bacot. One male lived 32 days and fertilized eighteen females 



As stated above, eggs will hatch in sixteen days at 25° C, bul 

 below 22° C. they usually do not hatch. How long a period of low tem 

 peratures they can endure, and still hatch when the temperature is agaii 

 raised, is not known beyond a statement by Nuttall that he delayed hatch 

 ing to 35 days by low temperatures. Certainly the safest plan would b( 

 to allow 30 to 40 days of cool weather or«two weeks of hot weather foj 

 all the eggs in discarded clothing to hatch. 



There are three larval stages, or possibly we may call the last th( 

 nymphal stage. The larvae suck blood from their human host. The firsi 

 molt occurs on the third to eighth day, and the other stages are corre 

 spondingly long. 



In molting, the skin splits longitudinally from base to apex o 

 thorax and along the base of the head to near the base of the palpi. 



The entire life cycle of corporis on the human body may be as shor 

 as sixteen days, eight for the egg, two each for the first and second larva 

 stages, three for the third stage, and one day preovipositional period 

 The head louse has been carried through its entire life cycle in seventeei 

 days. 



The frequency with which lice feed is dependent upon the rate of diges 

 tion, which is dependent upon climatic conditions. They feed more fre 

 quently at body temperatures than when kept cool. They feed at al 

 times of the day. Lice whicl^ have not had a feed for some time becomi 

 ravenous and often feed to excess, rupturing the intestines and causing 

 death. 



