LIFE HISTORY OF ASCARIS LUMBRICOIDES. 3 
Foster, 1917) also indicated that the theory that rats and mice act 
as intermediate hosts is not tenable. In fact it has become quite evi- 
dent that human beings and pigs become infected with Ascaris as a 
result of swallowing the eggs, the behavior of the parasites in rats 
and mice being simply the expression of an abortive development in 
animals imperfectly adapted as hosts. Our investigations have 
shown that the parasites migrate through the lungs in the guinea 
pig, rabbit, sheep, goat, pig, and presumably man, as well as in the 
rat and mouse. Very definite evidence has been obtained showing 
that the animals in which the parasites reach maturity become in- 
fected by swallowing the eggs, that the larve after hatching migrate 
out of the intestine into the lungs and back to the intestine, under- 
going a development similar to that which occurs in rats, mice, and 
other unsuitable hosts. Having returned to the intestine, following 
this migration, some of the young worms may be eliminated in the 
feces and perish, but others may establish themselves and complete 
their development to the adult stage. 
Stewart’s very striking discoveries therefore have not upset our 
former views of the life history of Ascaris so far as concerns the 
spread of the parasite from infested human beings and pigs to others, 
but they have added some highty important facts to our former im- 
perfect knowledge. Stewart, furthermore, has shown that the young 
worms not only migrate through the lungs, but in so doing may set 
up a serious pneumonia that in experimentally infected rats and 
mice is hable tc be fatal. The present writers, in a preliminary 
note already referred to (Ransom and Foster, 1917), noted the occur- 
rence of pneumonia in the pig as well as in smaller animals as a 
result of the invasion of the lungs by Ascaris larve, and Stewart in 
some of his later papers (1917, 1918) also reported Ascaris pneu- 
monia in pigs. It is evident that Ascaris may lkewise affect the 
lungs of human beings, and it is an interesting fact that Mosler 
(aceording to Leuckart, 1867) and Lutz (1888) in experiments in 
feeding Ascaris eggs to human subjects observed certain ling symp- 
toms undoubtedly to be attributed to Ascaris infection, though of 
course the significance of the symptoms was not appreciated at the 
time. It is not unhkely that many cases of lung disease of obscure 
nature may have as an etiological factor the invasion of the lungs 
by Ascaris larve. Lang affections in children especially should be 
studied with reference to this possibility. In the case of pigs the 
frequent and serious condition commonly known as “ thumps” is un- 
doubtedly often the result of Ascaris infection. Stewart’s contribu- 
tions to our knowledge of the life history of Ascaris may accordingly 
prove the starting point from which an important advance can be 
made along the line of disease prevention. 
