SOME HUMAN PARASITES 301 



have four pairs of legs, but with this exception they re- 

 semble spiders very little, They are widely distributed 

 over the earth wherever man has taken up his abode. 

 They are very minute, increase exceedingly fast, and 

 are most tenacious of life when once they have become 

 established on the human skin. Unfortunately, not as 

 much is known of the life history of these mites as is 

 desirable — probably because no one cares to act as 

 host for them as it would be necessary to do if one 

 wished to study them thoroughly. 



History of the itch disease. — This disease is very old, 

 in fact, is probably as old as man himself. It seems 

 quite probable that man contracted the disease, origi- 

 nally, from the lower animals with which he associated or 

 came in intimate contact. The itch mite of the horse 

 may be transmitted to man, but the infection is only tem- 

 porary — three to eight weeks. On the other hand, the 

 itch mite of the camel and goat, when transmitted to man, 

 may cause severe and persistent cases of itch. The mite 

 causing scabies on the hog and the dog may also thrive 

 for a time on man. In view of the ease with which these 

 itch mites from the lower animals thrive upon man, it is 

 not too much to believe that primitive man originally 

 contracted the disease from some animal with which he 

 came in close contact. Indeed, it is held that the itch 

 mites upon man and the lower animals are simply varieties 

 of the same mites and not distinct species. 



An Arabian physician, Avenzoar, in the twelfth century 

 seems to have been the first man to point out the true 

 cause of this malady. Other physicians in the fourteenth 

 and seventeenth centuries pointed out the real cause of 

 itch and in 1761 Linne very appropriately named the tiny 



