27O KATHARINE FOOT. 



for experiment and I have succeeded in securing the services of 

 a young French doctor who has just commenced to practice and 

 lives in a suburb of Paris where there is a large working class 

 and where the popular belief as to the advantages of lice is in 

 evidence. We are thus equipped to experiment not only with 

 medicated blood but with the external use of drugs, which method 

 of attack, however, has been so thoroughly tried and proved so 

 disappointing that there is very little inspiration for further 

 effort. I have repeated many of the experiments in the labor- 

 atory by apply mg the drugs on the area of the skin used in feed- 

 ing and these efforts have only confirmed the negative results of 

 other investigators. 



I also experimented placing relatively impervious substances 

 on the arm of. the host to determine whether the lice would be 

 aware of the human skin below and bite through the substance. 

 One experiment was interesting as indicating that the lice real- 

 ized the human odor. A piece of the skin of an apple was used 

 and it was scraped until the layer was so thin it was almost trans- 

 parent. After this was put on the arm of the host the lice were 

 placed on it and showed no indication of being conscious of the 

 proximity of the human skin they not only showed no effort to 

 bite but were indifferent and inert. After 30 minutes the apple 

 skin was reversed and the surface which had been next to the 

 human skin was placed uppermost. When the lice were placed 

 upon this surface their behavior was entirely different they 

 were very active, running excitedly around in the confined area 

 and this showing an indication of a sense of the human odor 

 which undoubtedly adhered to the surface of the apple skin which 

 had been for 30 minutes in contact with the arm of the host. The 

 lice however showed no effort to bite through this foreign sub- 

 stance, though the experiment seemed to indicate that they are 

 susceptible to an odor and is evidence in favor of the assertion 

 that they avoid some people and that this selection may have 

 some connection with a sense of smell. 



I was fortunate in securing an opportunity to experiment with 

 a case of this so-called immunity from attack by lice. 1 If we 

 1 See appendix, page 274. 



