520 



DISEASES OF CATTLE. 



and eye, and in the watery swellings which often develop under the 

 lower jaw (" poverty jaw"). If the fourth stojnacli of a dead animal 

 is cut open and the contents carefully examined, the parasites, which 

 axe from \ inch to 1^ inches in length and about as thick as an 

 ordinary pin, maj- be seen, if present in any considerable nmnber, 



actively wrigghng about like 

 little snakes. 



Cattle become infected with 

 these parasites by grazing on 

 pastures on which infested 

 cattle, sheep, or goats have 

 grazed and scattered their 

 droppings. The worms in the 

 stomach produce a multitude 

 of eggs (fig. 14c) of micro- 

 scopic size, which pass out of 

 the body in the feces. In 

 warm weather these eggs 

 hatch in a few horn's. If the 



• , - temperatme is below 40° F.. 



^ I they remain dormant, and if 



} H below freezing, they soon die. 



The eggs are also killed by ch'v- 

 ness; moisture, on the other 

 hand, favoring their develoj)- 

 ment. Thelarvji" whichhatch 

 from the eggs are microscopic 

 in size, and, like the eggs, are. 

 at first and until they have 

 developed to a certain stage. 

 ver^^ susceptible to freezing 

 and drying. In very warm 

 weather the larvte complete 

 their development, so far as 

 they are able to develop out- 

 side the body, in two or three 

 days. In cooler weather the 

 time requii-ed for this devel- 

 opment is longer, and at tem- 

 peratures below 70° F. 10 

 days to several weeks may be necessary. The larvae are then ready 

 to be taken into the body. Tlu^ eggs and early stages of the larva^ 

 apparently do not develop if swallowed, and only the coinplete<l 

 larval stage seems to be infectious. In this stage the larva> migrate 

 up grass stalks (fig. 15) or other objects, showing activity whenever 



Fui. 14.— Twisted stomach worms (Hiemonchut contniius) 

 Male (a), female ft», and cgf.' (ci. Knlarge<l. 



