214 the president's address. 



killed by a Sarcoptes, not from injury to any important organ ; they 

 simply die worn out by want of rest. In the French Army, after 

 the Franco-German War, the disease spread so suddenly amongst 

 the cavalry horses as to become very serious, and in this case, and 

 that of some other animals, as the camel, it was found that the 

 disease could be more or less communicated to the human atten- 

 dants, although it did not proceed far with them, soon dying out 

 without remedies. 



A marked contrast to the Sarcoptes is offered by the only other 

 Acarine true parasite of man, the Demodex folliculorum. This 

 curious little being, with its short legs and its long tail, is a per- 

 manent parasite, but a harmless one. It lives calmly from genera- 

 tion to generation inside the sebaceous follicles of our noses and in 

 our ears without our usually having the least idea of its presence. 

 It appears, however, to be otherwise in the pig and one or two 

 other animals, in whose skin a Demodex breeds in such quantities 

 as to produce a diseased state. 



A curious and very doubtful temporary parasite of man is the 

 so-called harvest-bug. If we go for a walk in late summer amongst 

 long, very dry grass we shall probably come home with an itching 

 on the calves of our legs, which will soon become intolerable. An 

 ordinary examination will possibly not disclose anything except 

 the result of our own scratching ; but careful study with a good 

 lens will reveal a number of small white pimples with a minute 

 scarlet demon seated on the top of each. This demon is the young 

 hexapod larva of some species of Trombidium, for he may belong to 

 any one of several species. A drop of turpentine will probably dis- 

 lodge him ; if left alone he will die a natural death in two or three 

 days. He is the Lcptus antumnalis of the earlier writers, who sup- 

 posed the six-legged mites to be separate genera, not knowing that 

 they were simply the larvae of the eight-legged mites. Why these 

 predatory creatures should leave their happy hunting-grounds 

 among the grass to fasten on to my leg I never could quite under- 

 stand ; it does not agree with them, for they die there. If they 

 were older they would have learnt wisdom, for the nymphs and 

 adults of the same species are not ever found adhering to the skin. 

 The irritation produced must probably result from some poison, not 

 from any wound so minute a creature can inflict ; and looking at 

 their close relationship to spiders, and their similar mode of life, 

 this seems probable. 



