THE LIFE HISTORY OF HUMAN LICE 



303 



infestation, has been reduced more than two-thirds. It is also well known 

 that immigration has been greatly reduced. 



Tlie urgency of the problem in the armies led to extensive investiga- 

 tions of control measures and of the biology of lice. The knowledge 

 of the biology of the body louse was surprisingly meager up to the time 

 the war began. It is our purpose in this lecture to call attention to some 

 of the vital points in the biology of lice, and to point out their relation 

 to practical control work, for without a knowledge of these points, one 

 cannot expect to intelligently interpret the results of control work. Some 



Fig. 61. — Wristlet method used for breeding lice. (Hutchison, Photo by Dovener.) 



of the more important and recent additions to our knowledge of louse 

 biology are due in no small measure to the improved technique for rearing 

 lice as evolved by Bacot, Sikora, and Nuttall. Warburton's method of 

 placing the insects on cloth in plugged tubes, feeding them twice daily 

 and placing the tube in the pocket or incubator between fecd^'has been 

 largely followed, with modifications by other workers, but after many 

 attempts at rearing lice under more normal conditions and providing them 

 with unlimited opportunities fo=r feeding, Nuttall finally worked out the 

 two methods which he describes under the names of the "felt cell method" 

 and the "wristlet method" (fig. 61). For the details of these methods it 

 is best to consult the original description in Nuttall's (191Tb) article on 

 the biology of Pediculus humanus. In fact, we have avoided giving a 



