198 
Ascaris lumbricoides 
That this assumption is correct is also proved in a remarkable manner 
by an experiment performed by Mosler (1860, as cited in Leuckart’s 
Menschl. Parasit. n. pt. 1. p. 222, from the original paper in Arch. Path. 
Anat. xviii. 249). Mosler, after a preliminary and negative experiment 
on himself, administered ripe eggs of A. lumbricoides to a number of 
children, at first in small numbers, but later several dozen to each 
child. No worms were at any time evacuated after anthelminthic 
treatment but in one (or two) of the children, fever with dyspnoea 
occurred a few days after the administration of the eggs. Leuckart 
adds that it is of course doubtful whether this fever was due to the 
experiment. There can now however be little doubt that the fever 
and dyspnoea were due to pulmonary ascariasis, the dose in one or two 
cases having probably exceeded several dozen 1 . 
III. We are then to consider the following facts, that ripe eggs of 
A. lumbricoides or suilla hatch in the intestine of their definitive hosts 
man or the pig, and also in the rat and mouse, and develop in the body 
of man and of these animals in an identical manner up to the 2 mm. 
larva in the trachea. Further that in the mouse the larvae then pass 
through the alimentary canal unharmed and are evacuated in the faeces. 
To cover these facts two hypotheses may be advanced: (a) That the 
normal development of the worm occurs in one host only, the definitive 
host, man or the pig, and that the larvae in the trachea of man or the 
pig pass through the oesophagus and stomach and become adult in 
the intestine and that the development in the rat and mouse is merely 
an accidental development in an abnormal host and is unconnected 
with the life history of the parasite. This hypothesis was advanced 
in an Editorial in the British Medical Journal, July 1st, 1916. (b) That 
the rat and mouse are intermediate hosts and that the larvae passed 
in the faeces of these rodents can, either at once or after further develop¬ 
ment, infect the definitive host. On this hypothesis it may or may not 
be necessary to assume that the larval development in man and the 
pig is accidental. It is conceivable that the definitive host is able to 
act as an (unusual) intermediate host in addition to and in substitution 
for the usual intermediate (the rodent). 
The former hypothesis is the simpler. It should be susceptible of 
proof or disproof by a moderately numerous series of experiments per¬ 
formed in the light of the facts I ha ve established, the experiment being 
1 It is difficult to understand why Mosler should have selected the human child as a 
subject for experiment in place of the pig. The use of the latter appears preferable both 
from the practical and moral standpoint. 
