TRICHINELLA SPIRALIS I DEVELOPMENT 317 



Later on adipose cells appear at their poles, and after about 

 six or nine months they commence to calcify, the process starting 

 at the poles (fig. 209). Finally, sometimes after the lapse of years, 

 the captive trichinellae themselves become calcified. 



According to experience, trichinellse are not found to be evenly 

 distributed in the muscular system of pigs ; the muscular parts of 

 the diaphragm, the muscles of the larynx, tongue, abdomen and 

 intercostal spaces are their favourite positions ; this predilection 

 for the respiratory muscles is explained by their regular contrac- 

 tions ; in addition, regular contractions of the capillaries take 

 place and favour the fixing of the circulating trichinellae. The 

 same circumstance probably explains the frequency of the parasites 

 in the tongue. 



Possibly also the trichinellae that bore direct through the 

 intestine may penetrate the muscles in the vicinity from the 

 abdominal cavity. Frequently also encysted trichinellae are found 

 in remarkable numbers in the vicinity of the points of insertion of 

 the tendons, this proclivity being probably connected with the 

 fact that the trichinellse first of all wander into the muscular 

 fibres and find a natural barrier at the points of insertion of the 

 tendons. 



The trichinellae, in their encysted condition, remain alive and 

 capable of development for many years. (In the pig eleven years 

 and in man twenty-five to thirty-one years.) Encyst ment, how- 

 ever, is not a necessary condition for the development of the 

 brood. 



In consequence of the new batches of young produced during several 

 weeks, the above-mentioned symptoms of disease are often considerably 

 aggravated ; the fever increases, delirium may arise, and infiltration of the 

 lungs, fatty degeneration of the liver and inflammation of the kidneys 

 may ensue ; the initial slight oedema may extend, the strength dwindles, 

 and in many cases the patients succumb to the trichinosis. In severe 

 cases improvement of the condition is only apt to occur in the fourth or 

 fifth week ; the convalescence is always protracted. 



The black rat and more particularly the sewer rat (Mm 

 rattus, Mus decumanus 1 ) are the normal hosts of ' Trichinella 

 spiralis. These animals, especially the last-named species, 2 infect 



1 It is still a matter of dispute and can hardly be definitely settled whether trichi- 

 nellaa were brought to Europe by the sewer rats which invaded Europe at the 

 end of the eighteenth century, or whether they were imported with the Chinese pig in 

 1820 or 1830, when it was introduced into England and Germany to cross with the 

 native breeds, or whether finally trichinellae are also indigenous to Europe. 



2 [The Sewer Rat is M. decumanus ; Mus rattus is the Black Rat. F.V.T.] 



