PARASITISM 125 



General treatment. — Medical treatment must be siu-h as will 

 destroy or remove the parasites. Medicines may aid in remov- 

 ing parasites by suffocating them, by poisoning them, or by caus- 

 tic or irritating chemical effect on the parasites. Many para- 

 sites disappear at a certain stage by means of their own activity 

 and habits; e.g., ticks, bots in horses, grubs in backs of cattle, 

 •and grubs in the nasal passages and head cavities of sheep. It 

 is well to remember also that many parasites, bots in the horse's 

 stomach for instance, can resist stronger medicines than the 

 organs or tissues they invade. 



Practical suggestions. — Parasitism would l)e impossible if 

 everything that comes in contact with the animal body were free 

 from parasites. Saddles, harness, blankets, posts, and fences 

 are the usual agents which spread Texas itch or mange among 

 horses; intestinal worms generally gain entrance in the egg or 

 immature form, with the food or drinking water. 



Parasitic diseases may often be prevented by forethought 

 and wise management. Intestinal parasites of sheep, like 

 stomach worms, module disease, tapeworms, etc., may be largely 

 prevented by change of grazing ground — pasture, meadow, 

 stubble, millet, sorghum, rape, etc. 



Serious trouble from lice in winter should be prevented by 

 proper treatment in the fall, while the weather is still warm 

 enough for vigorous treatment by dipping or w^ashing. 



In many cases, the parasite requires two hosts, living its im- 

 mature stage in one host, and its mature stage in another. Cer- 

 tain immature tape worms which cause losses in sheep, use the 

 dog for their mature form host. Unnecessary association of dogs 

 and sheep on feeding ground is therefore unwise. 



Ponds, wells which receive surface drainage, sluggish streams 

 and marshes, shoukl thei-efore be regarded with suspicion. 

 Sound animals should not be allowed in sheds, yards, or barns 

 where animals diseased by external parasites, like lice or scab 

 mites, have been, until such structures have been disinfected. 

 Intestinal worms w^hich appear in the manure of horses should 

 be destroyed with boiling water, — not merely crushed and 

 thrown aw^ay. 



External Parasites 



Lice. — These are wingless insects classified into two general 

 groups, biting lice and sucking lice. Each of these general 



