LIFE HISTORY OF ASCARIS LUMBRICOIDES AND 
RELATED FORMS 
[PRELIMINARY NOPE] 
By B. H. Ransom, Chief, and W. D. Foster, Junior Zoologist, Zoological Division, 
Bureau of Animal Industry, United States Department of Agriculture 
Recently Capt. F. H. Stewart, 1 of the Indian Medical Service, in 
several publications has recorded the results of some experiments of 
great importance in the light which they throw upon the question of the 
life history of Ascaris lumbricoides , the common intestinal roundworm of 
man. The same parasite, or a form so closely related that it is morpho¬ 
logically indistinguishable so far as our present knowledge goes, is of 
very common occurrence in the intestine of pigs (A. suum or A. suilla). 
Stewart used both forms in his experiments. He failed in his attempts 
to infect pigs but found that if rats or mice were fed Ascaris eggs, the 
eggs hatched in the alimentary tract, and the embryos migrated to 
the liver, spleen, and lungs. In the course of their migrations they 
increased in size and passed through certain developmental changes, 
many of them finally reaching the alimentary tract again by way of the 
lungs, trachea, and esophagus. The young worms that succeeded in 
regaining the alimentary tract did not continue their development and 
soon passed out of the body in the feces, so that rats or mice surviving 
the pneumonia commonly caused by the invasion of the lungs became 
free of the parasites as early as the sixteenth day after infection. 
As a result of his investigations Stewart was led to a conclusion con¬ 
trary to the usually accepted opinion thkt the infection of man or pig 
with Ascaris results from the ingestion of the eggs of the parasite. He 
concluded that it is necessary in the life cycle for the eggs to be swal¬ 
lowed by rats or mice and that in these animals the embryos hatching 
from the eggs undergo certain migrations and developmental changes, 
after which they may be transferred in the feces or saliva of the rats or 
mice to food or other materials likely to be ingested by human beings 
or pigs, and thus ultimately reach their final hosts. 
1 STS WART, F. H. ON THE LIFE-HISTORY OP ASCARIS LUMBRICOIDES. In Brit. Med. JoUT., 1916, V. 2, 
no. 2896, p. 5-7, 3 fig* 1916. 
- . THE LIFE-HISTORY OP ASCARIS lumbricoides. In Brit. Med. Jour., 1916, v. 2, no. 2909, p. 474. 
1916. 
- . FURTHER EXPERIMENTS ON ASCARIS INFECTION. In Brit. Med. Jour., 1916, V. 2, no. 2910, p. 
486-488,1916. 
- . on THE life-history of ascaris lumbricoides. In Brit. Med. Jour., 1916, v. 2, no. 2918, p. 
753-754. 1916. 
-. ON THE DEVELOPMENT OF ASCARIS LUMBRICOIDES LIN. AND ASCARIS SUILLA DUJ. IN THE RAT AND 
mouse. In Parasitology, v. 9, no. 2, p. 213-227, 9 fig*. 1 pi* i 9 * 7 * 
Journal of Agricultural Research, 
Washington, D. C. 
ky 
(39s) 
Vol. XI, No. 8 
Nov. 19, 1917 
Key No. A—32 
