440 MANUAL OF FARM ANIMALS 



as suggested on page 161, modified to meet the attendant con- 

 ditions. 



For convenience in discussing the common diseases of sheep, 

 we may divide them into four classes : those due to external 

 parasites, as scab, foot-rot, sore eyes, sore teats, tick, lice, and 

 the like; second, those due to internal parasites, as stomach- 

 worms, tape-worms, and the like; third, derangement of di- 

 gestion, due to improper feeding; and fourth, other diseases, 

 as caked udder, garget, catarrh, and the like. 



EXTERNAL PAEASITES 



The cure for external parasites is dipping. When done as sug- 

 gested in pages 423 to 427, it will completely eradicate such 

 parasites as ticks and lice as well as the pests that cause scab, 

 foot-rot, sore eyes, and sore teats. The prevention of any of 

 these parasites is a very simple matter. 



INTERNAL PARASITES 



Treating internal parasites is much more difficult. In many 

 cases the parasites are located where medicine cannot reach 

 them, as in the brain or liver; and even when located where 

 medicine can reach them, as in the stomach, the medicine is of 

 very little value as it is so diluted with digestive juices by the 

 time it reaches the worms. The only practical treatment is 

 prevention. This involves some trouble, and in order to make 

 the necessity for such clear, we will consider a case in detail. 

 Of course, dipping is of no avail for the internal parasites. 



The stomach-worm. — This worm (Strongylus contortus) is a 

 small, thread-like worm about three-fourths of an inch in length. 

 It lives in the fourth stomach, and especially afflicts lambs, at- 

 tacking them at any age after they begin to nibble grass until 

 cold weather in the fall. This stomach-worm is by far the most 

 destructive of parasites, doing more damage than all others 

 combined. When the fourth stomach of the lamb becomes filled 



