536 HORSE, SWINE AND POULTRY DISEASES 



the middle about one two hundred and fiftieth by one four thou- 

 sandth of an inch. 



The embryos begin to escape from the bodies of the females 

 into the intestine of the host about six days after infestation, and 

 the production of embryos may continue for a month or more but 

 abates considerably after the first few days. The adult worms usual- 

 ly disappear from the intestine in five or six weeks, or even sooner if 

 the patient is affected with diarrhea. The total number of embryos 

 which each female is able to produce has been estimated at 10,000 

 to 15,000. 



As soon as born the embryos begin to migrate, penetrating the 

 intestinal wall and entering the connective tissue, lymphatics, and 

 blood vessels. They are apparently aided in their migrations by 

 the blood current and are carried to various portions of the body, 

 finally entering the muscles. This period of migration lasts from 

 six to ten days. Having reached its final resting place in a muscle 

 the embryo grows considerably, reaching a length of 0.8 to 1 mm. 

 (about one thirtieth to one twenty-fifth of an inch) and a thickness 

 of about one six hundredth of an inch. In the meantime as it 

 grows the embryo coils itself into a spiral and becomes surrounded 

 by a membranous cyst, produced by changes in the interfascicular 

 connective tissue of the muscle, brought about in consequence of the 

 irritating influence of the worm. 



In form the trichina cyst is usually ovoid or lemonshaped, with 

 its long axis directed parallel with the muscle fibers. The average 

 fiize is about one sixtieth by one hundredth of an inch. After a time 

 fat globules are deposited on the outside of the cyst in little masses at 

 each pole. In seven or eight months after infestation the cysts begin 

 to degenerate, commonly becoming calcified, and the vitality of the 

 worms is finally destroyed. 



This process of degeneration is completed usually within about 

 two years, although cases are on record in which calcification of the 

 cysts was still very slight as long as eleven years after infestation, 

 and the worms were still alive. 



The number of encysted larvae which may be present in even 

 a small piece of muscle in cases of severe infestation is very large. 

 As many as 1,200 have been counted in a piece of muscle weighing 

 1 gram, which would make about 500,000 in a pound. If a person 

 were to eat a pound of pork thus heavily infested, and if all of the 

 larvae developed to maturity in his intestine, and if each female 

 produced the estimated number of 10,000 embryos, there would be 

 set free in the intestine 2,500,000,000 to 3,000,000,000 embryos. 

 Of course, in an actual case not all of the larvae would develop, and 

 not every female would produce as many embryos as assumed in 

 the estimate, nor would all the embryos succeed in penetrating the 

 intestinal wall and migrating into the muscles. The computation, 

 however, gives an idea of the great intensity which infestation may 

 reach. The number of cysts present in the bodies of persons who 

 have died with the disease has been estimated in various cases at 

 from 5,000,000 to 100,000,000. 



