ANIMAL PARASITISM 757 



ful in finding a host, the cercaria dies in a few hours, but if it comes 

 in contact with the skin of a man, or any other mammal, the cercaria 

 enters the skin, with the aid of glands in the head region which seem 

 to be used in digesting or destroying the skin tissues. After pene- 

 trating the skin the cercaria soon finds its way into a blood vessel 

 and begins a voyage through the circulatory systen, 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 





^ i 



f. 



Fig. 397. — ClonorcMs sinensis. Oriental liuman Uver fluke, showing male and 

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



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 'Egy])t, public clinics (by injecting fuadin 

 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. 



ClonorcMs 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 l| 



often causes enlargement of the liver, diarrhea, jaundice, anemia, 11 



and extreme weakness, sometimes resulting in death. Hundreds of 

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



