636 OCCURRENCE AND MEDICAL IMPORTANCE. 



While it is extremely rare that more than five or six Echinococci 

 develop in the liver or lungs of man (there are a few cases where 

 the liver contained twenty) one finds in the peritoneal coat of the 

 abdomen or in the omentum hardly a single example of a solitary 

 Echinococcus. 



After what has been proved in regard to the natural history of Tcenia 

 echinococcus, there can be no doubt as to the origin of the Echinococci. 

 The Echinococcus-bladdeis are descended from the tape-worm, and 

 where they occur an importation of the tape-worm brood must have 

 preceded, all creatures suffering from Echinococcus, whether man or 

 beast, must in some way or other have become infected with the eggs or 

 proglottidcs of the Tcenia, and have had the enclosed embryos liberated 

 by the action of the digestive juices. After their liberation these 

 embryos must have bored through the intestinal walls, * and have more 

 or less directly reached their subsequent position. This internal 

 wandering may be effected through the blood-vessels or lymphatics, 

 and this view is supported by the preference of the worms for the 

 liver, which is rendered easily accessible by virtue of the portal 

 circulation. That all the Echinococci are not found in the liver is no 

 contradiction, because the embryos may readily pass by the lymphatics 

 into the venous system. 



Since the Tcenia echinococcus inhabits especially the intestine of 

 the dog, and since the dog is the only host known to us which comes 

 into close association with man and domestic animals, ive can hardly 

 be in error if we regard it as the only source of the Echinococcus disease. 



We need hardly show how cattle, &c. may infect themselves with 

 the eggs or proglottides of T. echinococcus. The proglottides voided 

 by the dog so constantly and in such numbers for the tape- worm, as 

 we know, lives socially, and often occurs in thousands are either 

 eaten with the dung, as by swine, or are carried by their own and by 

 external movements on to substances which serve as food, and thence 

 into the intestine of cattle and other herbivorous animals. Sometimes 

 only the eggs and not the proglottides are thus transported, but the 

 result is the same, provided the eggs have not in the meantime lost 

 their power of development, or fallen into an unfavourable environment. 



But how are they introduced into man. Primarily, of course, and 

 most frequently, in consequence of accidental contact, as we explained, 

 in connection with Cysticercus cellulosce. In the latter case the infecting 

 material has its origin in man himself, in the present case in an animal 

 which lives near man, sharing lodging, food, and sometimes even bed 



1 I cannot support Neisser's idea that the six-hooked embryos are quite passive in their 

 transmission through the tissue, like silver grains in Argyriasis, since they are by no means 

 so motionless as Neisser seems to suppose. See p. 322. 



