Parasites of Muscular and Connective Tissue. 425 



Causes. These are mainly conditions that favor the reception 

 of the encysted trichina, by a host which can advance it to ma- 

 turity, and which can entertain the offspring in its own muscles 

 in turn. Certain chains play a most important part in this de- 

 velopment. 



The chain constituted by the pig on the one hand and the rat 

 (brown or black), mouse and other small rodents on the other, is 

 one of the most fundamental. This is especially noticed about 

 slaughter-houses or other places where the products of dead pigs 

 are handled. The rats and mice eating trichinous pork become 

 sick, stiff, lame and are easily caught and eaten by the hogs that 

 are kept to eat up the waste. Thus new hogs are infested and 

 the trouble moves around its vicious circle tending to a constantly 

 encreasing prevalence. 



In the same way hog is infected by hog, when a herd is kept at 

 or near a slaUghter-house to eat up the offal. 



Another cycle may be found through the manure of the infested, 

 containing the embryos. The dejections of infe.sted rats and 

 mice are taken in with the food, and the dejections of the in- 

 fested pigs are carried into their troughs by the snouts and feet, 

 or washed into pools, wells or streams from which they are sup- 

 plied. 



At Bamberg abbatoir 50 per cent of the rats were trichinous, 

 and at Boston slaughter-houses 76 per cent. In stables apart 

 from abbatoirs the ratio was from 7 to 10 per cent. only. In 

 country districts 2 to 3 per cent, is a high average for America 

 and great areas are entirely free from it. 



It must be recognized that rats will eat their own dead, so that 

 here we meet with another line of propagation. 



Man usually derives trichinae from pork, but here the cycle 

 usually ends as the hog cannot obtain human flesh. Yet in many 

 localities where hogs run at large and have access to human de- 

 fecations and to the water that has received drainage from these, 

 the pig still secures a contingent of trichina from man. 



Man may further be infested by meats, otherwise sound, which 

 have been laid or cut on the same chopping block, counter or 

 scales, by bread which has been cut by a knife which has just 

 been used for cutting raw pork, by contamination through kitchen 

 table or refrigerator, or by water which has received drainage 

 from dejections of affected men or animals. 



