DISSEMINATION OF BODY-LOUSE 35 



the problem of distributing themselves in a vast 

 variety of ways. Some, such as the bot-flies, 

 are in one stage immobile parasites, and in 

 another active flies which are able to seek out 

 and place their eggs on a fresh host. Some, 

 such as certain species of the hippoboscid flies, 

 which have a louse-like habit, are able to fly in 

 one stage and cast their wings, for which they 

 have no further use when they reach their fresh 

 prey. Certain species of fly, the maggots of 

 which live in the skin of mammals, have become 

 still more ingenious and lay their eggs where a 

 mosquito may accidentally pick them up and 

 carry them to another mammal. There are 

 others, to which group lice as a whole largely 

 belong, which rely more on the habits of their 

 hosts for their dissemination rather than on any 

 active habits of their own. If man radically 

 changed his habits in one or two particulars his 

 body-lice would cease to exist. This has already 

 been indicated in the history of civilised countries, 

 for it was the growing habit of constantly chang- 

 ing underclothing and paying more attention 

 to the toilet that reduced body-lice to so small 

 a frequency before the War. Now that stress of 

 circumstances has caused many millions of people 

 to revert in these respects to the habits of 

 mediaeval times, lice have come into their own 

 once more. 



The spread of lice is due, to some extent, to 

 their own active habits, for when their host is 



