TRICniNIASIS OF M.VN AND ANIMALS. 5 



may be met with not only in the abdominal cavity of the autosite, 

 but also in tlie thoracic and pericardial sac, and in such numbers 

 that these places may be looked upon as normal resting-places for 

 the embryos on their migrations ON'er the infected organism. In 

 general we lind them far more numerously represented in the ab- 

 dominal cavity, which corresponds exactly with our knowledge of 

 their activity, for it is here that they must first come after passing 

 the intestinal parietes on their migrations. From here they pass on 

 to the other cavities b}' means of the natural openings, or ostia, 

 through which the oesophagus and large vessels pass thi'ough the 

 diaphragm. These vessels are loosely surrounded by connective 

 tissue, which others favorable conditions for the passage of the para- 

 sites. From these cavities the embryos follow the course of the 

 larger vessels and nerves over the body, the loose connective tissue 

 offering the favorable conditions. The duration of the migratory 

 period can not be determined with any great degree of accuracy ; 

 but it is undoubtedly very short, as embryos have been found in 

 the thoracic cavity, the pericardial sac, and adjoining muscles, as 

 early as in the abdomen. The majority of observer seem to agree 

 in considering the ninth or tenth day of invasion as terminating the 

 migratory period — that is, when but a single invasion has taken 

 place." 



" The end)ryos display no distinguishable changes either in size 

 or structure during the period of migration. The first appreciable 

 changes occur after they have reached the muscles, and have be- 

 come lodged in their fibers." 



" When they have penetrated the fiber — that is, become intra- 

 sarcolemmatous — the protoplasma of the muscle-cell undergoes cer- 

 tain pathological changes, which exactly correspond to the fatty de- 

 generation observed in parenchymatous myositis. A proliferation of 

 the nuclei is quite common, if not an invariable phenomenon. Like 

 all tissues which have undergone fatty degeneration of their plasma, 

 such fibci-s are darker, less refracting, than those which have not 

 been subjected to parasitic invasion. Such fibers lose their con- 

 tractility. When cut transvei*sely, the swollen jiarenchyma extends 

 beyond the sarcolemmatous sheath, and if the trichina be near the 

 section, it often extends free, or becomes free, with the protruded 

 plasma. It is doubtful whether the triehinaj live upon the elements 

 of the plasma while lodged in the fii)er, as they are in an appar- 

 ently chrysalis condition. This fatty degeneration of the paren- 

 chyma seems to offer no impediment to a second invasion of the 

 fiber." 



