38 
Ascaris lumbricoides 
to be on the average less infected with Ascaris than pigs which were kept as 
controls, and had not been so fed. 
They summarise their results as follows: “Stewart’s observations as to 
the migration of Ascaris larvae through the lungs have been confirmed, but 
his suggestion that rats and mice act as intermediate hosts is not tenable. 
No intermediate host is necessary, and human beings and pigs become infected 
with Ascaris as a result of swallowing the eggs of the parasite, and not as the 
result of swallowing food, water or other substances that have been con¬ 
taminated by the faeces of rats and mice.” They base this view on the 
experiments referred to, and on the apparent death of larvae passed in the 
faeces of mice. 
[I wish to emphasize that this view rests on the discovery which I was the 
first to make and to publish (Stewart, 1917 a), namely, that the larval develop¬ 
ment of the worm can take place in pigs as well as in rodents. Since making 
this observation I have asserted the possibility of direct infection. I maintained, 
however, that the mode of infection had not yet been conclusively demon¬ 
strated, that it was possible that the larvae passed in the faeces of mice were 
not actually dead, but in a condition of suspended animation, and that 
consequently indirect infection might also be possible.] 
Ransom and Foster's paper is a very scholarly exposition of all work 
bearing on the subject. It contains sections on the relation of age to infesta¬ 
tion which also exhibits the high frequency of the parasite among swine in 
the United States, on the egg stages of A scans, and on the life-history of related 
Nematodes. Of great theoretical interest is the observation that the larvae 
of Ascaris anoura apparently pass through the lungs of its host—a python— 
and reach a much higher stage of development there than do the larvae of 
A. suilla in the lungs of the pig. 
In experiments on guinea-pigs the authors found Ascarid larvae in the 
lungs after the subcutaneous injection of ripe eggs of A. suilla. In feeding 
experiments they also found a small number of larvae in a few cases in the 
spleen and thyroid gland and under the peritoneum. They suggest the 
explanation that some young larvae may pass in the blood stream direct 
through the liver and lung, and thus entering the arterial system may be 
carried to situations remote from their normal route. 
(2) Sadao Yoshida (1919) finds that hatching and larval migration of 
A . lumbricoides take place in guinea-pigs, monkeys and rabbits, and that human 
beings can be infected by.larvae from the lungs of guinea-pigs. He has not 
yet completed the morphological study of the larvae. 
(3) In a second paper, Yoshida (1919 a) develops the thesis that the 
larvae migrate through the serous sacs and direct through the tissues, not 
along the blood stream. This view he bases (1) on experiments in which he 
injected larvae extracted from the organs of one animal into the serous sacs 
of a second, and thereafter recovered them from remote tissues of the second 
animal. (2) In another series of experiments he administered ripe eggs by 
