EXAMINATION OF CYSTICERCOID STAGES 163 



among their number. This species, with others related to it, possesses 

 the property of facultative parasitism, and has, on rare occasions, 

 adopted man as its host. 



Of the parasitic Nematodes which occur in Central Europe, the 

 one most readily obtainable is Oxyuris vermicular is. It is frequently 

 harboured by children, especially in the country, and is voided irr large 

 numbers with the faeces. The well-known " threadworms," which 

 move actively about upon the surface of the warm faeces, are female 

 Oxyures, the uteri of which are full of eggs containing embryos. They 

 should be handled with the greatest caution, as at this stage they are 

 very infectious. 



Trichinous pork is also an infective material which is easily 

 procured, though it is by no means as common now as formerly. 

 It should be cut parallel with the muscle-fibres into small pieces, and 

 these should be pressed between two glass slides. The Trichinae are 

 spirally coiled worms enclosed in lemon-shaped capsules ; they are 

 easily discoverable with a low power lens. Infection is rarely so 

 extreme that parasites are present in every piece of flesh, and it is 

 generally necessary to examine a large number of specimens before 

 finding proofs of disease. Even where infection is very advanced, large 

 portions of the muscular structure are frequently free from parasites, 

 though these may be present in large numbers in other muscles of the 

 host (diaphragm, pharynx, lingual, and intercostal muscles), or in 

 other parts of the same muscle, as, for instance, the point of attach- 

 ment of the tendons. Trichinae are very difficult to discover in flesh 

 which has been converted into sausage-meat, and detection here is 

 entirely a matter of chance ; hence, a negative finding is no proof of 

 immunity. 



In full-grown swine, the encapsuled Trichinae begin to calcify 

 about six to nine months after infection, though the process may 

 begin earlier, and it is, occasionally, omitted altogether. It com- 

 mences at the poles and about fifteen to sixteen months are required 

 for complete calcification of the capsule, which leaves the inmate 

 unaffected. This process of calcification, which extends in the course 

 of years to the inmate of the cyst, is part of the normal development 

 of the parasite and is rarely observed in swine, as these are generally 

 slaughtered in their first year. There is an analogous pathological 

 condition in which the worm dies and calcifies, either before or after 

 the formation of the capsule, the process of calcification subsequently 

 spreading to its surroundings. It should be borne in mind that the 

 Cysticerci which occur in the flesh of swine may also die and calcify. 

 They are readily distinguishable from calcified Trichinae by their larger 

 size and different shape, as well as by the presence of the cyst, which 

 is composed of connective tissue of varying thickness. 



