462 



Biology in America 



the wall of the intestine, and then migrate, probably through 

 the blood vessels to the muscles. Here they encyst, surround- 

 ing themselves with a capsule which is partly secreted by 

 themselves and partly by the irritated tissue surrounding* 

 them. If now, the improperly cooked flesh of a hog, infected 

 with these trichina is eaten by man or the rat, the sheaths are 

 dissolved by the digestive ferments of the second host and the 



^^.^ 



,.'"... .v 



Trichina Imbedded in Muscle 

 Courtrnii o} the U. .V. Bureau of Animal Industry. 



worms are set free in its intestine to repeat the cycle occurring 

 in the hog. It is during the course of their migration and en- 

 cystment in the muscles that occurs the terrible suffering 

 caused by this disease which is usually relieved by death 

 alone. If however the infection be light, the patient may 

 recover, the worms finally dying, and being absorbed, leaving 

 only the connective tissue scars to mark their place. Since 

 hogs rarely have the opportunity of eating human flesh the 

 rat becomes in one sense a necessary agent in the persistence 



