ECONOMIC ZOOLOGY. 403 



believe that this is the same as the human disease, or at 

 least that it is intercommunicable in man and cattle. 



403. Animals Hurtful to our Animal Friends. Our 



domestic animals are apparently almost as open to dis- 

 eases as man himself. Hence it is that there are many 

 animal diseases, caused by the various parasites of blood 

 and organs. The Texas fever of cattle; the haemoglo- 

 binuria of cattle and sheep ; pebrine, a disease of the silk- 

 worm; the sleeping sickness of Africa; etc., are due to pro- 

 tozoa, and are carried by ticks, flies, and the like. The liver- 

 rot and staggers of sheep, and the various tape- worm 

 and hook-worm diseases of hogs, dogs, cattle, and man 

 are caused by the unsegmented worms. The "bot" 

 diseases of horses, sheep, and cattle are produced by the 

 larval stages of flies. Mange, itch, etc., as found in various 

 domestic animals, is due to the action of mites. 



404. Animals Hurtful to Plants and Plant Products. 



At this point animals, more particularly the insects, do 

 great damage to man's interests. The story is too long 

 to tell here, but insects attack plants at every stage of 

 their history from the time they germinate until the 'time 

 they are stored. They devour foliage, fruits, timbers, 

 seeds, stored grain, and manufactured products. It is 

 said that "the elm has eighty species of insects that are 

 more or less supported by it ; birches and maples, over one 

 hundred ; corn is attacked by about two hundred species, 

 of which fifty do notable injury and some twenty are 

 pests; apple insects number some four hundred species." 

 It is estimated that the farmers and fruit growers of 

 America alone lose 500,000,000 dollars annually from 

 the ravages of insects on crops and forests. Man has 

 done much to control most animals except the insects, 



