142 PARASITOLOGY. 



constantly taking the sulphate of iron into the 

 intestinal tract it will create an unfavorable place for 

 the development and life of the worm. 



Oesophagostoma Columbianum (Columbia). 

 Syjionym. — Oesophagostome of Columbia. 

 Distribution. — Found commonly in the United 

 States. First discovered in the District of Columbia. 

 Description. — The worm is thread- 

 like in calibre, white in color, slightly 

 tapering anteriorly; the mouth is circu- 

 lar and provided with a double row of 

 teeth arranged in a crown -like form; 

 Fig. 52- the caudal pouch of the male is saucer- 



Oesophagostoma shaped ; the tail of the female termin- 



Columbianum . - , . .1 1 



a^ Male. ^tcs lu a rather sharp pomt ; the male 



b, Female. mcasurcs about three fourths of an 



inch in length, the female about oneinch. 

 Life Cycle. — The ovigerous female lays its eggs in 

 the intestinal tract, which find their way to the ex- 

 ternal world with the feces ; the embryos are taken 

 up by the host through the contaminated food and 

 water; upon reaching the intestinal tract they pene- 

 trate the mucous membrane and produce nodules 

 which are irregular in outline and vary in size up to 

 a pea ; these nodules are found in both small and 

 large intestines; often in badly infested cases em- 

 bryos are noted to invade the mesentery and mes- 

 enteric lymph glands and liver. The tumor, smaller 

 in size than a pin-head, contains a cyst in which is 

 found a growing embryo coiled in a ring-like shape, 

 floating in a colorless fluid ; in the second stage the 

 embryo is still in the cyst but a small quantity of 



