]50 VETERINARY STUDIES 



their natural destruction in much less than a year. They have 

 been shown to be capable of infection after several months. 



When the atmosphere is moist, embryos leave the manure 

 or earth and crawl up the moistened blades of grass or similar 

 objects, climbing only while there is moisture. If now they are 

 swallowed by a suitable host, the embryo continues develop- 

 ment for about three weeks, at which time the females may 

 begin to produce eggs. 



Symptoms. — There are no diagnostic symptoms by which this 

 disease can be distinguished from other internal parasitic dis- 

 eases of sheep. There is a gradually developing dullness, weak- 

 ness, and unthrift. Lambs are affected more seriously than 

 older sheep. These are usually unthrifty during the late sum- 

 mer, and some die during the late summer and fall. The most 

 common and evident symptoms are pallor, loss of flesh, and 

 weakness. The appetite is variable; affected sheep are usually 

 dull, listless, and often have unusual thirst and diarrhea. There 

 frequently appear swellings under the jaw. 



To make a certain diagnosis it is usually necessary to ex- 

 amine the carcass of sheep recently dead or kill a sick one for 

 this purpose. Examine very carefully the fourth stomach. If 

 this stomach is opened at the top and contents allowed to rest 

 quietly, the stomach worms, if present in sufficient numbers to 

 cause trouble, will be seen in quite active motion, wiggling about 

 like tiny snakes. They may sometimes be found in very large 

 numbers close to the lining membrane as slender reddish worms 

 varying from one half to about one inch in length. If the 

 fourth stomach be emptied and the worms are present in large 

 numbers, some may be seen attached to the mucous mem- 

 brane. 



Management of infected flocks. — An infected pasture may be 

 safe after a year if there has been no use by sheep in the inter- 

 val. Burning over a pasture is very efficient for the ground 

 actually burned over. A pasture that has been plowed and 

 cropped one season is usually safe. Freezing kills eggs and 

 early stage embryos. 



In dealing with an infected flock, we may treat both the lambs 

 and their mothers, beginning with the ewes early in the season 

 before the lambs are old enough to treat. The death loss may 

 thus be prevented and the lambs do much better. It should be 

 clear that there is no way of rapidly eradicating stomach worms 



