ENTOZOA. 63 



The cysts are very readily detected, by gently compressing a thin 

 slice of the infected muscle between two pieces of glass and applying 

 a magnifying power of an inch focus. They are of an elliptical 

 figure, with the extremities m.ore or less attenuated, often unequally 

 elongated, and always more opake than the body or intermediate 

 part of the cyst, which is, in general, sufficiently transparent to show 

 that it contains a minute coiled-up worm. The usual size of the 

 cyst is 3^oth of an inch in the long diameter, and ^^Y^yoth of an inch 

 across their middle part. The cysts are always arranged with their 

 long axis parallel to the course of the muscular fibres, which probably 

 results from their yielding to the pressure of the contained worm, and 

 becoming elongated at the two points where the separation of the 

 muscular fasciculi most readily takes place, and offers least resistance. 



The innermost layer of the cyst can sometimes be detached entire, 

 like a distinct cyst, from the outer portion, and its contour is gener- 

 ally well marked when seen by transmitted light. By cutting off 

 the extremity of the cyst, which may be done with a cataract needle 

 or fine knife, and gently pressing on the opposite extremity, the 

 Trichina and the granular secretion with which it is surrounded, will 

 escape ; and it frequently starts out as soon as the cyst is opened. 



When first extracted, the Trichina is usually disposed in two or 

 two and a half spiral coils ; when straightened out it measures J^th of 

 an inch in length and -yo o*^ ^^ ^^ ^^^^ ^^ diameter, and now requires 

 for its satisfactory examination a magnifying power of at least 200 

 linear admeasurement. 



The worm is cylindrical and filiform, terminating obtusely at both 

 extremities, which are of unequal sizes ; tapering towards one end 

 for about one-fourth part of its length, but continuing of uniform 

 diameter from that point to the opposite extremity. 



Until lately it was only at the larger extremity that I have been 

 able to distinguish an indication of an orifice ; and this is situated in 

 many specimens in the centre of a transverse, bilabiate, linear mouth. 



The anterior third of the alimentary canal is more even than the re- 

 maining part, which presents a sacculated appearance ; in this respect, 

 the Trichina resembles the newly excluded young of Ascarides and 

 Strongyli. A small rounded cluster of granules of a darker or more 

 opake nature than the rest of the body is situated about one-fifth of 

 the length of the animal from the larger or anterior extremity, and 

 extends about half-way across the body. 



The worm has no organic connection with the cyst: sometimes 

 two TrichifKB, rarely three, occur in the same cyst. 



The Medina or Guinea-worm {Filaria medinensis Gmel.) is de- 

 veloped in the subcutaneous cellular texture, generally in the lower 



