30 BU'LLETIK" 817^ U. S. DEPT. OF AGRICULTURE. 



The worms have always been apparently underdeveloped, which has 

 led some to hold the opinion that the sheep ascarids which resemble 

 Ascark lumhrlcoides are imperfectly grown worms of this species, 

 or of AscaHs svMm if the pig Ascaris is considered distinct from 

 the hmnan Ascaris. In view of the experience of the writers in 

 artificially infecting a lamb by feeding the eggs of the pig Ascaris 

 it would appear that the common opinion as to the identity of the 

 sheep Ascaris is correct. As further evidence of the ability of species 

 of Ascaris to undergo at least a partial development in the intes- 

 tine of a strange host may be cited the results of our experiment in 

 feeding Ascaris simni eggs to a young goat, and it may also be noted 

 that Jammes and Martin (1906) record the development of Ascaris 

 vitulorvmi in the human intestine to a length of 8 mm. One of these 

 writers swallowed A. vitulorum eggs and recovered the young worms 

 in his feces 25 days later. 



LIFE HISTORY OF RELATED NEMATODES. 



The migration of the larvae of intestinal parasites through the 

 lungs of the host before they finally settle down in the intestine is 

 not peculiar to Ascaris. It has been shown by Looss and others that 

 the larvse of hookworms and of, Strongyloides^ after entering the 

 host through the skin, migrate to the lungs through the heart by way 

 of the lymphatics and blood vessels, and then pass up the trachea 

 and down the esophagus, finally reaching the intestine. 



The senior writer has observed the larvae of Hmrrhonchus contortus 

 (stomach worm of ruminants) in the lung of a guinea pig killed 48 

 hours after it had been fed a culture of the larvae, which indicates 

 that they are able to migrate from the alimentary tract to the lungs 

 and perhaps do so normally in their life cycle in their usual hosts, 

 sheep, cattle, etc. 



In view of the fact that the larvae of forms belonging to diverse 

 genera, Ancylostoma^ Strongyloides.) Ascaris.) and, perhaps, HcBmoTi- 

 chus^ regularly migrate through the lungs before establishing them- 

 selves in the intestine, it is quite likely that the phenomenon is one 

 of common occurrence in the life cycle of parasitic nematodes. It 

 is to be expected, certainly, that forms closely related to Ascaris 

 lumbricoides will act similarly with respect to the migration of the 

 larvae through the lungs. Stewart (1918a, p. 194) found the larvae of 

 Belascaris marginata in the liver of mice 1 to 3 days after they had 

 been fed ^^^^ of this parasite. The present writers have fed the eggs 

 of Belascaris marginata to rats and 5 days later have found the larvae 

 in the lungs. The lungg showed petechial hemorrhages similar to 

 those observed in the lungs of animals invaded by the larvae of 

 Ascaris luml^ricoldes or Ascaris suum (Experiment No. 8). 



