DISEASES OF CATTLE 353 



that the micro-organism of malaria is carried by the mosquito, and 

 that various forms of pathegenic bacteria are scattered far and wide 

 by the fly. The micro-organism of Texas cattle fever is known be- 

 ycnd a doubt to be carried by the cattle tick. 



As carriers of other parasites, the flea and louse of the dog are 

 known to carry the larval form of one or more of the species of 

 the tapeworm of the dog. The dog, in licking, or biting itself to 

 destroy the parasites, or to relieve himself of the irritation, swallows 

 some of them, and the result is the development of an adult tapeworm 

 in the digestive tract. 



The losses due to parasites can not be estimated with any degree 

 of accuracy. As a rule, no notice is taken of their presence until 

 the animal begins to lose flesh, yet during all this while a greater 

 quantity of blood has been necessary to supply the parasite with nour- 

 ishment and to supply the animal with a sufficient quantity to com- 

 pensate the tissues for that which has been extracted by the parasite. 



Considering all classes of parasites, the deaths therefrom are 

 numerous, especially in sheep, in reference to which it may be 

 stated that three-fourths of the deaths are due to some form of 

 parasitism. In some parts of the South, especially in the lower 

 Mississippi valley, the loss from the buffalo gnat has been enormous. 

 Osborn states that in a single county in Tennessee the loss from this 

 cause in 1874 was $500,000. 



It is a popular notion that only poor animals are infested with 

 parasites and that the fat animal is exempt. Such a notion has 

 probably gained credence because parasites are not suspected, or 

 looked for, until the animal is noticed to be in an unthrifty con- 

 dition. It is a fact, however, that the fattest animal may be infested 

 with lice when a poor animal in the same herd may be free from 

 them. It should be remembered that lice seldom attract attention 

 until they become so numerous that the animals begin to lose flesh. 

 Another idea is that white cattle are most frequently infested with 

 lice. Such is probably not the case, but owing to the fact that lice 

 are more easily seen among the hair of a white animal than on 

 those of other colors, attention may more frequently be attracted 

 to the white animal. It is, however, asserted by a number of obser- 

 vant stock men that animals of a certain color are more frequently 

 attacked by lice. This may be true to a certain extent, and, if true, 

 the reason can not at this time be explained except that the skin 

 of certain individuals of certain color may be thinner and more 

 easily penetrated by the biting or sucking mouth parts of the lice. 

 It is hardly reasonable to suppose, however, that if a louse cast its 

 lot on the skin of one individual he will perish, or leave his host 

 in search of a more tender one. It is a well known fact, however, 

 that certain individuals among the human family are almost en- 

 tirely exempt from attacks of harvest mites, or giggers, while 

 others are greatly annoyed by them ; which in all probability is due 

 to some peculiar condition of the skin or its secretion. 



The fact that certain species of lice, and other parasites, will 

 only infest certain species of animals is due no doubt to some differ- 



