DISSEMINATION OF BODY-LOUSE 37 



legs not very well adapted for travelling on 

 anything except rough cloth or hair. Peacock (1) 

 showed that it is improbable that they are 

 attracted to man in any way by his smell, since 

 they took no notice of a sweat-impregnated 

 shirt placed near them. They are guided in 

 their movements, to some extent, by a sensitive- 

 ness to light. When well fed they creep into 

 dark places, but hunger drives them towards 

 the light again. This habit, however, helps them 

 little in their search. They are very sensitive 

 to heat, being adapted to the temperature which 

 exists between the skin and the clothing. 86- 

 90 F., and what guidance they get in finding 

 a new host they probably obtain from this faculty 

 alone. Stray lice in a bed very quickly find a 

 man who sleeps in it. The temperature of their 

 surroundings has a profound influence upon 

 their movements and vitality. At 104 F. they 

 are extraordinarily active, running round and 

 round with the rapidity of bed-bugs. At 90 F. 

 they are moderately active, and if unable to feed, 

 digest what food is in them and succumb about 

 the second day from starvation. At the tempera- 

 ture of a warm room, about 70 F., their activity 

 is little marked, and their vitality is so reduced 

 that they may survive a week without food. At 

 still lower temperatures they become moribund 

 and die slowly, some having been known to survive 

 ten days at the freezing-point, and this is the 

 longest period which lice have been known to live 



