228 THE FLUKES 



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 known to be parasitic in man is Yokagawa 

 yokagawa, named after a Japanese parasitologist. It is widely 

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

 probably other oriental countries. It infects mice and dogs as 

 well as man. The whole life history is unknown but the encysted 

 cercarise are known to occur in the " ayu," a Japanese fresh-water 

 fish which is commonly eaten raw, and in a number of other kinds 

 of fish. 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 cer- 

 cariae 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 1 days. Y. yokagawa inhabits 

 the upper portion of the small intestine, sometimes in consider- 

 able 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 ^V 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 in a variety of animals from Egypt to 

 Japan, and occasionally parasitizes man. Two species of Echi- 

 nostoma normally parasitic in other animals occur occasionally 



