108 



The Naturalist. 



which, for their development into perfect animals, required some 

 other habitat : considering it to be not unlikely that the further 

 developmeiit might take place in the intestinal canal of some 

 carnivorous animal. He caused some of the specimens to be given to 

 various dogs and cats ; the result of these experiments was just as 

 anticipated by Dr. Gairdner. When magnified, the white specks in 

 the muscle are seen to be cysts of an oval shape, sufficiently transpa- 

 rent to show that they contain a minute coiled-up worm ; on 

 separating the muscular fibre, the cysts are foimd to adhere to the 

 surrounding substance very strongly, so as often to render it difficult 

 to detach them. They measure usually about ^^^^h of an inch in 

 length by x-g-oth of an inch in breadth, and are generally in single 

 rows parallel to the fibres of the muscle. If a thin section of the muscle 

 is dried, and mounted as a microscopic object with Canada balsam 

 in the ordinary way, the cysts become more transparent, and show the 

 enclosed worm very plainly ; a few of the cysts are seen to contain 

 two, and occasionally three distinct worms. The body of the parasite 

 is covered with a transparent skin, which seems to be almost, if not 

 quite structureless ; beneath this is a layer of fine granular matter, 

 having the appearance of stripes and corpuscles : this is considered to 

 be the muscular structure of the Trichina. The alimentary canal 

 extends through the whole body from the narrow end, or head, to the 

 extremity. 



It is said by many that the organs of generation do not seem to 

 exist in the encysted worm, but are developed when the Trichina 

 attain their full development in the alimentary canal of their host. I 

 believe the sex is frequently discoverable even when in the cyst. It 

 was at one time supposed that Trichina^ as found in the muscles, was 

 the larva of another animal, but experience has shown that the fully- 

 developed Trichina is a distinct species occupying the alimentary 

 canal, giving birth to young Trichina which pierce the walls of the 

 intestines, and on reaching the muscles, become capsulated. 



In the pig, thousands of Trichina may exist without affecting the 

 animal's health, though commonly at the period of migration from 

 the alimentary canal to the muscular system, there is a lassitude and 

 feverish state, which may be so severe as to kill, or may pass off, and 

 either the animal lives on with Trichina in its flesh, which afterwards 

 die, or in a short time there is evidence ot pain and debility, followed 

 by death. As many as from 50,000 to 80,000 Trichina have been 

 found in a cubic inch of human muscle. 



