314 THE ANIMAL PARASITES OF MAN 



were able by renewed experiments to demonstrate the cycle of develop- 

 ment of Trichinella spiralis. Similar investigations followed by Claus in 

 Wiirzburg, Davaine in Paris, Fuchs and Pagenstecher in Heidelberg, &c., 

 &c. 



Hardly had Zenker's case been published than numerous observations 

 on trichinosis in man appeared, some referring to isolated cases, others to 

 small or great epidemics, and nearly all from North Germany. The worst 

 epidemic was that of Hadersleben (1865) in which place, numbering hardly 

 2,000 inhabitants, 337 persons were taken ill within a short time, and of 

 these 101 died. The source of infection proved to be a single pig, the flesh 

 of which had been mixed with that of three other pigs ; 200 of the badly- 

 infected persons had exclusively eaten raw pork. 



Moreover, it soon became clear that epidemics of trichinosis had been 

 observed in Germany prior to 1860, but that their nature had not been 

 recognised, although in a few cases trichinellae had been found in the 

 muscles of those who had succumbed. 



HISTORY OF THE DEVELOPMENT OF Trichinella spiralis. 



Shortly after their introduction into the intestine of experimental 

 animals the encysted trichinellae escape from their capsules, which 

 are destroyed by the gastric juices, and they then enter the 

 duodenum and jejunum, where they become adult. During this 

 period they do not grow considerably, the males grow from o - 8 

 ro mm. to 1-2 1*5 mm. ; the females to 1*5 1'8 mm. Soon after 

 copulation, which already takes place in the course of two days, 

 the males die off; the females, which during the following days 

 attain a length of 3 3 '5 mm., either bore more or less deeply 

 into the villi, or by means of the Lieberkiihn's glands actually pene- 

 trate into the mucous membrane (Askanazy, Cerfontaine, Geisse), 

 and thus usually attain the lymphatic spaces. A few also pierce 

 through the intestinal wall and are found in the mesentery and 

 its lymphatic glands. They deposit their young, the number of 

 which, according to Leuckart, averages at least 1,500, in the lymph 

 spaces ; the newly-born larvae measure 0*09 o'l mm. in length, 

 0*006 mm. in diameter ; and they do not appear to increase in 

 size during their migrations. The migrations are mostly passive, 

 that is to say, the larvae are carried along by the lymph 

 stream or by the circulating blood, but sometimes they are active, 

 as may be inferred from the fact that young trichinellae are found 

 in various parts of the intestinal wall beyond the chyle and. lymph 

 spaces, as well as free in the abdominal cavity. 



The young brood is distributed throughout the entire body, 

 but the conditions necessary to its further development are found 



