NOTES ON PEDICULUS VESTIMENTI. 27! 



could find a genuine case of immunity, it is self-evident that a 

 discovery of its cause might be of a great practical value. 



The case I was able to study was that of an intelligent Amer- 

 ican soldier (Sergeant Du R.) from one of our Western States. 

 He was thoroughly convinced that lice avoided him while attack- 

 ing his companions with whom he was in close contact. As 

 stated in my report he had been in France two years, was 

 many months at the front and frequently exposed to the pest. 

 He slept with his brother for about 3 months, during which 

 period his brother was infested with P. vestimenti and suffered 

 greatly. Later he slept for two weeks between two soldiers who 

 were infested and the lice were also in the blankets. At no time 

 was he bitten, nor did he find lice on his person, though he fre- 

 quently searched for them. 



In investigating his case my first disappointment was to find 

 that the lice by no means refused to bite him, but apparently 

 found him as tempting a host as any of the nine I had used in 

 my breeding experiments. The next step was to attempt to find 

 some explanation of his assumed immunity from attack. The 

 first surmise was that he might be classed with those cases in 

 which the bite is not followed by itching, and therefore he lacked 

 the unmistakable evidence of their presence and was deceived 

 as to his immunity. That explanation was quickly proved erro- 

 neous, for the itching from the bites was normal and very dis- 

 tressing. 



A second search for an explanation was to test whether the lice 

 could bite on all parts of Du R.'s arm, for if even a portion of 

 his skin were abnormally thick it might give him at least some 

 protection from attack. In my experience lice cannot bite 

 through skin that is a bit callous, such as the distal end of the 

 thumb and certain parts of the palm of the hand. Both adults 

 and nymphs were fed on various areas of Du R.'s arm from the 

 wrist to the shoulder and the biting was entirely normal in each 

 case. 



The two above mentioned suppositions could be easily tested 

 but it was not possible to give a conclusive answer as to whether 

 Du R.'s blood was sufficiently injurious to the lice to be offered 

 in evidence of his claim that he was immune from attack and he 



