CHAPTER VIII 



TRICHINELLA SPIRALIS AND RELATED 

 FORMS 



TECHNICAL SUGGESTIONS 



The importance of Trichinella spiralis as a parasite of man and 

 animals and the ease with which all stages of its life history may 

 be demonstrated make it especially desirable for laboratory study. 

 Other representatives of the group may be demonstrated. The 

 characteristic eggs of Trichuris should be studied. 



The most convenient sources of Trichinella for feeding experiments 

 are wild rats from slaughter houses, particularly from local establish- 

 ments. Here the infection may run as high as 75 per cent, though 

 such high incidence is exceptional. Another convenient reservoir is 

 the vagrant cat. Pork samples are not to be relied on unless a 

 considerable number, from different sources, are available. 



The presence of the parasite is best determined by the microscopic 

 examination of thin fragments of muscle from the diaphragm or 

 from the base of the tongue, cut parallel with the fibers and examined 

 under pressure. In the absence of a regular "trichina compressor" 

 a very satisfactory substitute is furnished by two slides clipped together 

 by spring clothes-pins. When an infection is located, bits of the 

 muscle should be fed to white rats or mice, and one of these should be 

 killed within 2 or 3 days for the study of the mature sexes isolated by 

 the method described on page 108. A second should be examined 

 2 or 3 weeks later for wandering larvse, and a third after 3 weeks for 

 encapsuled larvse. Calcified cysts will be present in muscle which has 

 been infected for 6 months or longer. 



Permanent mounts of these various stages should be made. Adult 

 worms should be killed in hot 70 per cent alcohol, and gradually 

 dehydrated and, after clearing in xylol, brought into thin balsam; 

 or they may be mounted in glycerine gelatine and sealed, as described 

 on page 105. Muscle containing the migratory stages may be 

 macerated for 24 to 48 hours in 0.1 per cent chromic acid or 2 per 

 cent acetic acid, teased, dehydrated, and mounted in balsam. For 

 the cyst stages compressed muscle may be dehydrated and mounted 

 in balsam; or it may be fixed, imbedded in paraffin, and sectioned. 

 For ordinary study it is undesirable to stain the material. 



To show the female worms in situ, the small intestine of a heavily 

 infected rat should be removed a week or more after the experimental 

 feeding, fixed in Bouin's fluid, sectioned, stained, and mounted 

 by the usual methods. 



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