Parasites of Muscular and Contiective Tissue. 423 



countries, and when real may be traced to the conditions under 

 which the hogs are raised. The idea that the trichina was absent 

 from Europe until the 19th century, is untenable. It was demon- 

 strated there as elsewhere when the microscope was brought to 

 bear on the muscles of man and pig. One hypothesis is that the 

 brown rat (mus decumanus) brought the parasite with him when 

 he migrated from Asia, and another that it was introduced in the 

 Chinese pig which was imported into England in the third decade 

 of the 19th century and into Germany on the fourth (Gerlach). 

 But Peacock's specimen in Guy's Hospital, already old and 

 calcified when found, dates back to 1828, and Tiedemann's to 

 1821. Trichiuous pigs have been found in Europe, North and 

 South America, China, Hindostan, Syria, Algiers, and elsewhere. 



Life History. Successive Habitats ; Migrations. The tri- 

 china only reaches sexual maturity in the intestines of a suitable 

 host. It may pass through the intestine of an unsuitable host 

 like a fish or reptile without losing vitality (Colin), and the same 

 appears to be true of certain birds the muscles of which do not 

 become infested. Expelled from the bowels in the liquid faeces 

 the mature worms soon perish, while the embryos may live for an 

 indefinite period in water, and communicate trichinosis to suscepti- 

 ble animals which drink it. The ovigerous female is often found 

 in the intestinal follicles, in the agminated and solitary glands 

 (Pagensticker) and even in the mesentery and mesenteric glands 

 (Cerfontaine, Askanazy) in which accordingly the young can be 

 brought forth. 



The embryos whether produced in the intestines, gland follicles, 

 mesentery or lymph glands, or introduced in drinking water are 

 the real migratory trichinae. They have been found to a very 

 limited extent in the blood, in which they can be carried to the 

 most distant parts of the body, but they appear to advance mainly 

 along the lymph spaces in the connective tissue and lymph ves- 

 sels. This explains their relatively greater numbers, both early 

 and late, in the diaphragm, lumbar and abdominal muscles. 



When trichinous flesh is introduced into the stomach it is di- 

 gested and the trichinae set free in five to twenty hours, the greater 

 number at the earlier period. The larva once freed from its cyst, 

 attains sexual maturity in one, two or three days more, and fully 

 ripened embryos are found in the womb of some females in four 



