464 ZOOLOGY. 



family acari or mites ; they are very small, and several live 

 as parasites on other animals. One species, the ixodes of 

 Brazil, fixes itself on dogs, oxen, &c., and so deeply plunges 

 its suckers into the flesh of these animals, that they cannot 

 be detached without raising up the portion of the skin to 

 which they adhere. It is asserted that the multiplication of 

 these parasites is sometimes so considerable as to cause the 

 death of the oxen and horses to which they have fixed them- 

 selves, by exhaustion.* Another kind of mite, called leptus 

 autumnalis, or rouget, is very common in the autumn in our 

 fields, and, insinuating itself under the skin of the legs, 

 causes insupportable itchings. Finally, it is a small animal 



Fig. 503. Sarcopt of the Psora (magnified) ; Itch Insect. 



of this family which, by multiplying in winding burrows 

 under the skin, occasions one of the most disgusting diseases, 

 the Psora, or Itch. The sarcopt of the Psora (Fig. 503) is 

 scarcely visible to the naked eye ; but when examined with a 

 microscope, its body is seen to be oblong, and its mouth to 



* Parasitical animals of this class abound in Southern Africa, and I am 

 aware that they attach themselves indiscriminately to oxen, horses, dogs, 

 &c., but it seemed to me that they had a predilection for the diseased or 

 enfeebled animal ; for if by chance an exhausted horse was left on the field 

 for some days, he became covered with these vermin, whilst they seldom 

 attached themselves to the healthy, well-fed animal. K. K. 



