318 THE ANIMAL PARASITES OF MAN 



themselves very easily, as they do not spare the members of their 

 own family, and they also transmit trichinosis to other species by 

 which they are devoured, such as pigs, dogs, cats, foxes, bears 

 and martens. Man becomes infected with trichinella by eating the 

 flesh, insufficiently cooked, of infected pigs, also, but more rarely, 

 by eating the infected flesh of wild boars, dogs, cats, bears and foxes. 



The infection of pigs may likewise take place by their having access to 

 the offal of trichinous pigs or being actually fed on it. These are, how- 

 ever, exceptions which, as a matter of course, are of great importance in 

 certain places. As a matter of fact the rats examined for trichinella were 

 always found to be severely infected. Thus Billings, in the knacker's yard 

 at Boston, found that 76 per cent, of the rats were infected, and in an 

 export slaughter-house 100 per cent, were found to harbour the parasite ; 

 in the City of Boston 10 per cent, of the rats had trichinosis. Heljcr 

 found that of 704 rats, from 29 different places in Saxony, Bavaria, 

 Wurtemberg and Austria, 8-3 per cent, were infected with trichinellae ; of 

 the rats caught in the knacker's yards 22- 1 were diseased ; of those taken 

 in slaughter-houses 2-3 were infected, and of rats from other localities only 

 0-3 per cent, harboured the parasite. Leisering found almost the same 

 figures, but in rats from slaughter-houses 5*3 per cent, were infected. 



The geographical distribution of Trichinella spiralis does not 

 correspond with the occurrence of trichinosis in man ; local customs 

 are an important factor, for instance, the custom of eating pork in a 

 condition that does not affect the life of the enclosed trichinella. 

 In places where such customs do not prevail epidemics do not 

 occur, at the most there are isolated cases of the disease, although 

 there be a great number of infected pigs. The following condi- 

 tions prevail in North America : In Boston, Billings found that 

 4 5'7 per cent, of the pigs examined were trichinous ; Belfield 

 and Atwood found that 8 per cent, were infected in Chicago. 

 Salmon found on an average that 2*7 per cent, were infected (but 

 at various places the percentage fluctuated between 0*28 16*3 

 per cent.), yet epidemics of trichinosis hardly ever occur in North 

 America, and only isolated cases of the disease are met with in 

 ; German immigrants, who keep to their native customs. 



This report, according to the researches of H. U. Williams, must be 

 considerably modified. This author has examined the muscular system of 

 human cadavers according to the method employed by inspectors of meat 

 for pigs. The investigations were conducted in the Pathological Institute 

 of the University of Buffalo, and the observer has examined 505 bodies 

 since 1894, of which 27 (= 5-34 per cent.) were invaded by trichinella. 

 The cases, according to the nationality, are divided as follows : 



