AXIMAL PARASITES OF CATTLE. 523 



rejected. It is especially important that the bluestone and water be 

 accurateh^ weighed and measured, and that the size of the dose be 

 graduated according to the age of the animal. 



The special value of medicated salts advertised under various trade 

 names as preventives against worms is problematical. Commonly 

 they contain little else than ordinary salt, the other substances being 

 in such small quantity that their therapeutic effect is practically 

 negligible. Definite evidence that they are more efficacious than 

 plain salt is not yet available and their use is not recommended. 



THE ENCYSTED STOMACH WORM (OSTERTAGIA OSTERTAGI). 



This parasite is as thick as a fine hair and less than half au inch in 

 length. It lives in small cysts in the wall of the fourth stomach 

 (fig. 17) and is also found free in the 

 cavity of the stomach. ^Vllen numer- 

 ous, these parasites cause a thickening 

 of the stomach wall and disturb its 

 digestive functions. The symptoms 

 caused by this parasite are very simi- 

 lar to those produced by the tA\'isted 

 stomach worm. The life history of the 

 encysted stomach worm is not knowTi 

 in detail, but it is undoubtedly very 



much the same as that of the twisted fig. 17.-Piece of lining of fourth stomach, 

 stomach worm. The same measures showingcystsoftheencystedstomachwonn 



as recommended above for preventing (^*'"<'^'« '^"''''"J'^- 

 infection with the twisted stomach worm should be used. Medicinal 

 treatment would seem to be of little use, owing to the protected posi- 

 tion in which the parasite occurs. 



INTESTINAL PARASITES. 

 TAPEWORMS. 



Two species of tapeworms (fig. 18) are known to occur in the small 

 intestine of American cattle. They sometimes grow to a length of 

 several yards and to a breadth of three-fourths of an inch. Small 

 portions of tapeworms, consisting of one or more segments, are oc- 

 casionally seen in the droppings of infested cattle. The life history 

 is not kno^vn, but the infectious stage is undoubtedly taken in with 

 the feed or water, infection being spread by the eggs of the parasite 

 contained in the feces of infested anunals. The eggs are perhaps 

 swallowed by some small creature (an insect, worm, or snail) which 

 acts as an intermediate host, and which when accidentally swallowed 

 by a cow while grazing or drinking carries with it into her stomacli 

 the infectious stage of the tapeworm. 



