472 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
an indirect life cycle. He assumed that some terrestrial imverte- 
brate—an insect, slug, snail, or other creature, not even excluding 
a mammal—harbored the intermediate stage which, he supposed, 
developed in it from the embryonated eggs it had swallowed, and that 
man became infected by accidentally eating with a salad, for instance, 
the alleged intermediate host. Von Linstow (14) actually pointed the 
finger of suspicion at myriapods that were abundant in vegetable 
gardens in Germany, and he assumed that the accidental ingestion 
of these invertebrates, especially by children, could account for the 
acquisition of the worms. Leuckart (13) finally receded from the 
position that A. dwmbricoides was a heteroxenous nematode, partly 
because he failed, despite repeated efforts, to find an intermediate 
host, but also because he was convinced that the epidemiological and 
experimental evidence marshaled by Lutz (15) did not support his 
assumption of an indirect life cycle. 
A new method of approach to the experimental study of the mode 
of infection of A. dwmbricoides was introduced by Davaine (1, 2) by 
using a rat as a test host. Twelve hours after administering in milk 
a large number of embryonated Ascaris eggs to a rat, this animal was 
destroyed and its digestive tract slit open and carefully examined. 
Although the eggs so administered had been kept in water for a 
period of 5 years, they were still alive. At autopsy of the rat, un- 
hatched eggs were still present in its stomach and duodenum. In the 
jejunum, and especially in the ileum, Davaine found living larvae 
that had extricated themselves from the egg shells, and some that 
were in the process of so doing through a perforation at one of its 
poles. The empty shells were ruptured but not digested. In experi- 
ments with another rat, Davaine observed living larvae that had 
passed out with the feces. From these experiments he inferred that 
Ascaris eggs probably would hatch in the human intestine, and the 
liberated larvae would grow to maturity there, without the interven- 
tion of an intermediate host postulated by Leuckart and von Linstow. 
NEWER KNOWLEDGE OF LIFE CYCLE 
And so matters stood until 1916. In that year, Capt. F. H. Stewart 
(23, 24) of the Medical Corps of the British Army, was stationed in 
Hong Kong, where Ascaris was very common in children and in pigs. 
Stewart published in the July 1, 1916, issue of the British Medical 
Journal an account of a series of remarkable experiments that gave 
an insight into the developmental cycle of A. Jumbricoides that was far 
different from that anyone had ever suspected. In fact, his experi- 
ments, as subsequent events showed, made it possible, for the first 
time, to place a correct interpretation on the results of Mosler’s ex- 
periments with one or two children who became ill with pulmonary 
