6 THE DISEASES OF DOMESTIC ANIMALS. 



" "While previous to migration the embryo shows a somewhat 

 slender form, it soon becomes thicker, or more rotund, its trans- 

 verse diameter being nearly double that which it had before migra- 

 tion. Its anterior portion becomes more slender and resembles that 

 of the mature parasite. The posterior end becomes more blunt. 

 Progressive changes also take place in the axial line, the different 

 organs becoming distinct ; especially is this the case in the cell- 

 body. The primitive sexual gland is to be seen as an elongated 

 sac ; the pointed anterior end extends beyond the stomach in the 

 females, and turns abruptly backward in the males. The oval cav- 

 ity has a proportionate length, and over its middle distinctly shows 

 the first traces of a nervous system, which in the form of an oval 

 enlargement, cervical ganglion, is to be distinguished from the cy- 

 lindrical mass." 



" With the progressive development of the internal organs comes 

 a corresponding increase of the external dimensions of the parasite. 

 It increases more in length than thickness, and its previous rotund 

 form becomes more slender. At the same time the body becomes 

 curved, and after a while assumes an irregular, spiral position — 

 trichina spiralis. They begin to assume this position the earliest in 

 the larger fibers ; but it occurs in all, even when the lumen scarcely 

 exceeds the transverse diameter of the parasite. In the vicinity 

 of the parasite the sarcolemmatous sheath invariably becomes dis- 

 tended, owing to the lateral pressure exerted by the parasite. The 

 spindle shape of the tube is due to the elasticity of the sarcolemma ; 

 but, as it becomes thicker and clouded, proliferation must take place 

 as well. The intra-sarcolemmatous, or capsular, development of the 

 parasite terminates in about three weeks from the time of its in- 

 vasion of the fiber." 



" The enlargements of the sarcolemma — capsules — vary much 

 in form and size. Sometimes they are far more cylindrical and 

 elongated than at others, and again one end may be elongated and 

 the other bluntly rounded." 



" The capsules are surrounded by a rete of capillaries, which can 

 be injected. A growth in length and thickness, due to the irrita- 

 tion caused by the parasite, gives them a very ramified character." 



In this condition the parasites are known as " muscle trichinse " ; 

 but when in the intestines of an autosite, as " intestinal trichinae." 

 In the first form they make their abode entirely in the striated, or 

 motory, muscles — the flesh. They have not been met with in an 

 encapsulated condition, either in the non-striated muscles or in 

 purely adipose tissue. 



