414 The Animal Kingdom 



the snails, and then swim about until they find a suitable fish host, usually 

 a minnow or carp. They bore into the flesh or at times under the scales, 

 and the metacercariae develop. Human beings eating uncooked fish 

 ingest the parasite. Within a few hours, the metacercariae are liberated 

 and the fluke is at home within the bile duct. Continued infections pro- 

 duce all manner of complications by clogging the bile duct and producing 

 liver cirrhosis. Often the pancreas is likewise infected. Extreme in- 

 fections as may occur gradually result in debilitation of the person, and 

 bacterial infections are easily acquired. 



This life cycle may at first sight seem so complicated as to be very 

 difiicult to complete. But human habits and the life cycle of Opisthorchis 

 sinensis work very nicely together. Throughout the Orient, the latrines 

 are placed over the fish ponds. The feces simply fall into the water ; 

 the snails and fish are already there and flourish on the free meals. Fuel 

 is a scarce commodity, and anyway people love their raw fish with sliced 

 vegetables. Thus the life history goes merrily along, and has little 

 chance of being stopped in the congested, tradition-bound Orient. 



Other Parasitic Flukes. — Other human parasites are lung flukes 

 of the genus Paragonimus. These are chiefly found in the Orient, but 

 are known from Yucatan and Peru. The adults of this fluke live in the 

 bronchial passages of the lungs and liberate their eggs which are then 

 passed out with the sputum. Miracidia develop from the eggs and 

 hatch in about three weeks' time. If these miracidia find a suitable 

 snail, they burrow in and produce sporocysts and rediae. About seventy 

 or eighty days later, the cercariae escape and creep in a leechlike manner. 

 If they find a suitable host, preferably a fresh-water crab or cray- 

 fish, they encyst and produce metacercariae in the muscles or heart 

 region. If an uncooked and infected crab or crayfish is eaten, the 

 worms are liberated in the intestine, burrow into the abdominal cavity, 

 and make their way through the diaphragm into the lungs. The general 

 symptoms of infection of Paragonimus are somewhat similar to those 

 of tuberculosis, that is, the sputum has blood in it and there is much 

 intermittent coughing. Some discomfiture also is usually experienced. 

 The infection is not fatal, and may persist for many years. 



Related forms with similar life histories are serious pests of mink 

 and other fur-bearing carnivores of our northern fur farms. 



Another human parasite of the Orient is Fasciolopsis biiski. The 

 adult of this fluke lives in the intestine of man and pigs. The eggs 

 pass out with the feces, the miracidia bore into a suitable snail host, 



