PARASITES OF ANIMALS. 113 



The females are larger and more numerous than the males, 

 and become about one-eighth of an inch long when full grown. 

 They pair as soon as mature, and the males soon die ; 

 but the females begin to give birth to living young in five 

 or six days from the time when they enter the stomach, 

 and they live long enough to produce a brood of from five hun- 

 dred to one thousand young worms each. As one ounce of pork 

 sometimes contains a quarter of a million or more of the worms, 

 it is not surprising that the millions of adult worms and their 

 offspring, sometimes resulting from a single meal of raw 

 pork, should, by their presence, produce great irritation and 

 inflammation of the intestine and violent diarrhoea and vomit- 

 ing, which are often the first symptoms in severe cases. But 

 the young worms, almost as soon as born, begin to eat or 

 force their way through the membranes of ' the intestine into 

 the minute blood-vessels and other organs, thus vastly in- 

 creasing the irritation. Entering the circulation they 

 are carried by the blood to the heart, thence to the lungs, 

 and then become diffused through the whole system. Accord- 

 ing to other observers, the young worms force their way di- 

 rectly through the intestine and all other intervening organs, 

 until they finally reach a suitable habitation in the voluntary 

 muscles. It is, however, difficult to understand how they can 

 become so evenly and generally distributed through the whole 

 muscular system as they often are, if this be their only mode 

 of diffusing themselves. It is, therefore, not improbable that 

 they migrate by both these methods, part entering the circu- 

 lation and part going directly through the tissues, while in 

 either case, if they find themselves in an unfavorable locality, 

 they have the power of changing their position while still in 

 the free state. According to Dr. Leuckart, they travel by the 

 way of the intermuscular connective tissues, and are found 

 most abundantly in the groups of muscles nearest the abdomi- 

 nal cavity, especially in those that are smallest and have the 

 most connective tissue. 



Effects. 



Large numbers often lodge in the heart, lungs, and various 

 other organs, producing great irritation and various danger- 

 15 



