396 
Journal of Agricultural Research 
Vol. XI, No. 8 
In reviewing Stewart's work it appeared to us that, granting the 
correctness of his observations, the conclusions that he had drawn did 
not supply an adequate explanation of the mode of infection 
with Ascaris. On a number of occasions we had endeavored*to infect 
pigs with Ascaris by feeding the and eggs, although the results of these 
attempts had been negative or uncertain and thus in harmony with the 
experience of Stewart and other investigators, we nevertheless did not 
feel justified in accepting these results as evidence against the hypothesis 
of a direct development without an intermediate host, nor did it seem 
that Stewart's experiments with rats and mice were sufficient to lead to 
the conclusion that these animals act in any way as intermediate hosts 
in the life cycle of the parasite. 
Repetition of Stewart's experiments in feeding rats and mice with 
Ascaris eggs gave results agreeing very closely with those which he has 
recorded. We have noted wider variations as to the time at which the 
larvae may be found in various organs and have observed them*in sev¬ 
eral locations in addition to those in which they were seen by Stewart, 
but the results of our experiments were essentially the same as his, and 
point to a migration of the larvae to the liver, lungs, spleen, and other 
organs, and finally from the lungs to the alimentary tract by way of the 
air passages through the trachea and into the esophagus, during which 
migrations they undergo considerable development and structural change 
and increase to a size of 1.5 mm. or more in length. 1 In most of our 
experiments the eggs of the pig Ascaris were used, as Ascaris from pigs 
was more easily obtainable than parasites from human beings. In addi¬ 
tion to our experiments on rats and mice we made further attempts, 
with negative results, to infect pigs. 
Our unsuccessful attempts to infect pigs by feeding Ascaris eggs were 
made on animals several months old. 2 It is noteworthy that Epstein, 3 
in his carefully controlled experiments with A. lumbricoides used very 
young subjects and that the positive results which he obtained can 
scarcely be explained upon any other assumption than that a direct de¬ 
velopment of the parasites occurred following feeding of the eggs—that is, 
development without an intermediate host. The experience of one of us (B. 
H. R.) in certain investigations 4 on the life history of Syngamustrachealis, 
our failures, and the failures of others to infect pigs with Ascaris, the fail- 
1 Since the preparation of this manuscript further investigations have shown that guinea pigs as well as 
rats and mice may be infected by feeding Ascaris eggs. In these animals the migration of the larvae 
was, as far as observed, identical with that noted by Stewart for rats and mice. All of the six infected 
guinea pigs died from pneumonia between seven and eight days .after feeding with Ascaris eggs, the 
lungs being heavily infested with Ascaris larvae. 
3 The pigs which Stewart used with negative results were stated by him to have been 2 months old. 
The ages of the animals us^i by various other investigators who failed to obtain positive results in experi¬ 
ments to bring about infestations by feeding the eggs of Ascaris are generally not stated, but in many of 
the negative experiments with human beings it is clear that adults were used as subjects. 
8 Epstein, Alois, ueber die uebertragung des menschuchen spulwurms (ascaris lumbricoides). 
In Verhandl. Versamml. Gesell. Kinderh. Deut. Naturf. u. Aerzte, v. 9, 1891, p. 1-16. 1892. 
4 Not yet published. 
