554 THE ANIMAL PARASITES OF MAN 



indebted to v. Zenker whose labors have proven that rats become infected by 

 the ingestion of other animals containing trichina. Contagion occurs in pigs, 

 as a rule, by " eating trichina-containing meat of other pigs." As is well 

 known, some parts of the meat are often utilized for feeding swine, particu- 

 larly during slaughter time in the country, and when- animals are skinned offal 

 containing trichina is often given to pigs. In such localities it is obvious that 

 sufficient waste material remains to infect at the same time the entire colony 

 of rats that are present. The latter continue to be for years a further source 

 of infection for the pigs, who are usually expert rat catchers, and who often 

 eat the enemy which they have killed. Wherever pigs infected with trichina 

 are slaughtered without the complete destruction of their cadavers, there is 

 danger of distribution of trichina. Mature trichinae are found in the small 

 intestine of the rat, the wild boar, the fox, the polecat, the marten, the raccoon 

 and the cat, as well as in man and in swine. Man infects himself almost 

 exclusively by the ingestion of raw or insufficiently cooked pork, which con- 

 tains the so-called muscle trichina in a condition capable of development. 

 Thorough boiling or frying will kill the trichina, provided the temperature 

 in the inner portions of the meat is 50° to 55° E. Neither decomposition nor 

 cold diminishes the property of life in the trichina. Muscle trichinae retain 

 their power of development for many years (up to 31). Thorough salting de- 

 stroys the life of the trichina, but it is certainly not destroyed by cold smoking 

 nor in the so-called rapid smoking process. 



The encapsulated trichinee found in the musculature appear as small gray 

 nodules, rarely over 1 mm. in length, and consist of a capsule which, as in the 

 case of man, after the lapse of years becomes calcified. The capsule encloses 

 the trichina. This is a spiral worm of 0.6-1 mm. in length and 0.01-0.03 mm. 

 in breadth ; the head is pointed, the tail is rounded ; upon the head is the mouth 

 opening, upon the tail the anus. If parts of muscles permeated with living 

 trichinas reach the stomach of man, of the pig or of any other suitable animal, 

 the gastric juice dissolves the capsule; in from two to three days the para- 

 sites which have entered the intestine attain their sexual maturity. Soon 

 after copulation the males die, while the females, according to the observations 

 of Askanazy, actively bore into the intestinal mucous membrane, and seven 

 to nine days after infection has taken place produce living young. This act of 

 bringing forth takes place usually in the tissue of the intestinal mucous mem- 

 brane, that is, close to the central chyle vessels of the villi. Probably the 

 majority of the embryos enter the circulation directly through the chyle and 

 lymph- vessels; carried by the blood-stream they wander into the transverse 

 striped muscles. Up to this time the usual mode of distribution has been 

 assumed to be migration, i. e., by boring through the intestinal walls, the para- 

 sites enter the peritoneal cavity, and thence the connective tissue parts of the 

 musculature ; or the path has been traced through the submucosa, through the 

 mesentery, and the retroperitoneal connective tissue. According to Askanazy, 

 distribution of the parasites by active wandering is only secondary. About 

 the ninth or the tenth day after infection, the first influx of parasites reaches 

 the musculature. The female is so immensely reproductive that, for about 

 seven weeks, new groups of parasites constantly find their way there. 



