Nov. 19, 1917 
Life History of Ascaris lumbricoides 
397 
ures of various investigators to infect adult human beings, and Epstein’s 
positive results in the case of young subjects, suggested the possibility 
that age is an important factor influencing the susceptibility of human 
beings and pigs to infection with Ascaris, and that many of the failures to 
bring about experimental infections would not have occurred if younger 
animals had been used as subjects. Our belief in this possibility was 
strengthened by the discovery of an Ascaris larva in a fragment of lung 
from a pig about 6 weeks old which had died from unknown causes 
in May, 1917, a finding which indicated a migration of larvae like that 
which occurs in rats and mice. The intestine of this pig contained 
numerous immature ascarids, the largest about 5 cm. long. In order to 
test the possibility of infecting very young pigs, after several disappoint¬ 
ments because certain sows reserved for the purpose of providing young 
pigs for experimental use either failed to farrow or devoured their new¬ 
born offspring, we finally succeeded in obtaining two young pigs from a 
sow which was found by fecal examination to be free from egg-producing 
ascarids. In the latter part of September, at the age of about 2 weeks, one 
of these pigs was given a large number of Ascaris eggs containing motile 
vermiform embryos. The number of eggs given was not determined, but 
there must have been at least several thousand. One week after feeding 
the pig which had been fed with Ascaris eggs was brought into the labora¬ 
tory dead; death had occurred either the same day or late the day before; 
in any event, approximately one week had elapsed since the animal had 
been given a heavy dose of Ascaris eggs. The other pig continued in good 
health. Examination of the dead pig revealed a pneumonia, with numer¬ 
ous petechial hemorrhages in the lung tissue. Numerous ascarid larvae, 
varying in length from 0.7 to 1.2 mm. in length, were found in the lungs, 
trachea, and pharynx; none in the liver, spleen, esophagus, small intes¬ 
tine, or large intestine. 
It is of interest to note in this connection that when rats or mice are 
fed large numbers of Ascaris eggs they commonly die of pneumonia 
about a week later, at a time when numerous larvae are present in the 
lungs, exactly as in the case of this pig. These findings are interpreted 
by us as clearly demonstrating that Ascaris larvae in young pigs, pre¬ 
sumably also in children, behave in much the same way as in rats or mice, 
and strongly support the hypothesis that the migrations and develop¬ 
ment of the parasites are very similar in the two cases, the only impor¬ 
tant difference being that in rats or mice the worms are unable to con¬ 
tinue Jtheir development to maturity. 
Stewart’s very important discoveries concerning the behavior of 
Ascaris larvae in rats and mice, the various contributions of other inves¬ 
tigators toward the solution of the problem of the life history of A. 
lumbricoides and related parasites, and our own experiences outlined 
above, appear to justify certain conclusions, some of which in anticipation 
