NOTES ON PEDICULUS VESTIMENTI. 269 



dictory results," and this he thinks is due to the small broods of 

 the experiments. This criticism justly applies to Hindle's re- 

 sults, whose conclusions are not convincing because they are 

 drawn from broods which in no case reached 50 per cent, of a 

 normal generation. The number of individuals in his 25 broods 

 quoted by Nuttall are as follows: 2, 4, 6, 9, 9, 10, n, 12, 15, 17, 

 24, 25, 26, 27, 29, 30, 31, 32, 34, 36, 38, 45, 48, 64. 



Nuttall ('17) found the sexes nearly equal, though his broods 

 also were small. My own results are in harmony with Nuttall's 

 though I am able to give only one brood in evidence. In this one 

 experiment, however, I attempted to determine the sex of every 

 individual that was hatched and succeeding with 92 per cent, of 

 a brood of 125 lice. This was made possible by using a slightly 

 different method from that of other investigators. As stated in 

 my report (Foot, '19), "Instead of waiting for the nymphs to 

 mature in order to determine the sex they were dissected at any 

 stage that was convenient and those that died were not discarded 

 but dissected at once and their sex recorded." One hundred and 

 twenty-five eggs were hatched and the sex determined for one 

 hundred and fifteen (62 males and 53 females). Should repeated 

 experiments with sodium salicylate show that the females in- 

 variably predominate we might then conclude that the drug is in 

 fact more injurious to the males, for Hindle's broods were either 

 all males, all females or males and females. If therefore a drug 

 constantly effects one sex it must be injurious whether the sexes 

 are normally equal per Nuttall or variably unequal per Hindle. 



The most practical method of testing a drug and of testing the 

 possibility of selection by the lice is to find a family where all 

 the members are infested and to select one member for experi- 

 ment. This is not as difficult as one would suppose, for there is 

 a popular belief among the most ignorant class that lice are con- 

 ducive to health that their relation to disease is not only pre- 

 ventive but curative. These people, therefore, welcome them as 

 friendly guests a degree of hospitality it is difficult to under- 

 stand. That this belief actually exists is proved by the fact that 

 a generous bribe is needed to induce the host to face the possi- 

 bility of any treatment causing his lice to decamp. 



It is self-evident that this situation affords an ideal opportunity 



