ANIMAL PARASITES 45 



medical schools of London. When examined with reflected 

 light rather than by transmitted light, they appear chalky white. 

 Study the demonstration specimens if you do not have a slide 

 showing this stage. 



Adults. — When trichinous flesh is ingested by man or other 

 appropriate host, the capsules are dissolved by the gastric 

 juice and the larvae are liberated. If you have infected meat 

 for study, some of it should be subjected to the action of an 

 artificial gastric juice and kept at body temperature for a day 

 or so, in order to obtain the free larvae. Other portions should 

 be fed to white rats or mice for study of the mature stages and 

 the migratory larvae. If such trichinous flesh is not at hand 

 and not procurable, use the prepared slides which will be 

 furnished. 



Within 48 hours after being ingested the larvae have developed 

 into mature sexual individuals. Examine fresh or mounted 

 preparations and observe the division of the body into the slender, 

 elongate anterior end and the posterior swollen portion. Note 

 the large cells making up the anterior portion and the delicate 

 oesophagus piercing them. The more conspicuous alimentary 

 tract of the swollen section opens by a terminal anus. 



In the female worms the eggs may be seen in progressive 

 development as they are traced forward from the posterior 

 region to the vulva in the anterior fourth of the worm, through 

 which the fully formed larvae escape. 



The males are only about half the size of the mature females 

 and are readily distinguished by the presence of two caudal, 

 hemispherical copulatory lobes. Between them are four minute 

 papillae. 



Make drawings illustrating the structure of the male and female 

 worms. 



Migrating Larvae. — By the end of the first week, larvae are 

 escaping in large numbers and are being carried by the blood 

 stream and, to some extent, actively migrating to the muscular 

 tissue. Tease parallel with the fibers small fragments of muscle 

 from an animal which has been infected 2 to 3 weeks previously. 

 Thus the still unencapsuled larvae can be obtained in numbers. 

 By the end of the third week cysts are being formed and the flesh 

 is infective for new hosts. 



Trichuris trichiura. — Examine the demonstration specimens 

 of the whipworm of man (T. trichiura) or of the related species 



