228 THE FLUKES 



is a serious hindrance to the sanitary disposal of such infected 

 material. Leiper suggests that this problem may be solved by a 

 chemical treatment of night soil which would destroy all parasite 

 eggs or cysts and yet not injure its value as a fertilizer. 



Intestinal Flukes 



There are several species of flukes which appear to be common 

 parasites of the human intestine in certain parts of the world, 

 especially in the oriental countries where the other human flukes 

 abound the most. Many of these flukes are very small, but they 

 may occur in great numbers, producing practically the same effects 

 as do tapeworms, anemia, emaciation and general debility. 

 Many species are probably only accidental human parasites, 

 normally living in some other host but occasionally finding their 

 way into the human intestine with food or water and establishing 

 themselves there. 



The smallest fluke parasitic in man is Yokagawa (or Metagonimus) 

 yokagawa, named after a Japanese parasitologist. It is widely 

 distributed in Japan, Korea, Formosa, parts of China, and prob- 

 ably other oriental countries. It infects mice and dogs as well 

 as man. Muto infected fish with the encysted cercerise by feed- 

 ing to them cercaria-infected snails, Melania libertina. Encysted 

 cercarise occur in a number of Japanese fresh-water fishes which 

 are commonly eaten raw, particularly the "ayu". The cysts are 

 most numerous in the connective tissue under the skin and about 

 the fins, especially early in the season, indicating that the fish 

 become infected by free-swimming cercarise which bore through 

 the skin, and not by cercarise eaten with another host. The 

 encysted cercarise closely resemble those of Clonorchis sinensis. 

 The development in the final host is said to take only from seven 

 to ten days. Y. yokagawa inhabits the upper portion of the small 

 intestine, sometimes in considerable numbers, but it never seems 

 to do enough damage to cause more than a slight intestinal catarrh. 

 It is remarkable for the lack of a ventral sucker and is only about 

 1 mm. (about -^ of an inch) in length, and about half as broad. 

 Its body is covered with a great many microscopic spines. 



A very similar fluke, Heterophyes heterophyes (Fig. 62), only 

 slightly larger, occurs from Egypt to Japan in a variety of 

 animals and occasionally parasitizes man. Two species of Echi- 



