ANIMAL PARASITISM 449 



and begins a voyage through the circulatory system, carried along by 

 the current of the blood stream, meantime growing into an adult 

 fluke. The mating of males and females usually occurs in the larger 

 veins, and the pair moves to the veins in the walls of the rectum and 

 bladder, where egg-laying begins. 



Irrigated districts, such as the Nile Delta, are especially favorable 

 for the development of blood flukes because the eggs have more 

 chance of getting into water and because the field workers often get 

 into the water while working around the irrigation ditches. The 

 chances of infection are increased by the customs of defecating and 

 urinating into the water, and using water from irrigation ditches for 

 drinking and washing. In Japan the number of human blood fluke 

 cases has been greatly decreased by improved sanitation and by 

 killing the host snails. In Egypt, public clinics (by injecting fuadin 



Fig-, 190. — GlonorcMs sinensis. Oriental human liver fluke, showing male and 

 female reproductive organs. (Photomicrograph by Albert EJ. Galigher, Inc.) 



into the blood) treat thousands of cases of this disease, but it will 

 probably remain a public health problem for years because of the 

 refusal of the Egyptian peasants to change their old customs. 



Clonorchis sinensis, the Chinese Liver Fluke. — This is an impor- 

 tant human parasite in parts of the Orient. Clonorchis sinensis also 

 occurs in other fish-eating mammals, including dogs, cats, and pigs. 

 The adult worm lives in the bile passages of the liver. In man it 

 often causes enlargement of the liver, diarrhea, jaundice, anemia, 

 and extreme weakness, sometimes resulting in death. Hundreds of 

 worms may be found in a badly infected man. The eggs laid by the 

 adults pass from the liver to the intestine of the host by way of the 

 bile duct, then pass from the body in the feces. Snails probably be- 

 come infected by swallowing the eggs, while feeding on fecal matter 

 in the water. After hatching, the miracidia migrate into the lymph 

 spaces of the snail and develop into elongated sporocysts, each of 

 which gives birth to a number of redia (differing from sporocysts by 



