F. H. Stewart 
199 
directed of course to ascertain whether after an infection in the pig in 
which Ascaris larvae are known to have reached the lungs, adult worms 
are found in the intestine after the lapse of a suitable interval. Now 
since the larvae cannot be demonstrated in the lungs without putting 
an end to the experiment, what criteria can be employed to judge of 
their presence in that situation? (1) The appearance of symptoms of 
pneumonia between the 7th and 10th days after the administration of 
the eggs may be regarded as proof positive. (2) Pulmonary infection 
appears to follow so constantly on the administration of an active 
culture of eggs both in rodents and in the pig, that if a culture is proved 
infective for a mouse it may be assumed that it will prove equally so 
for the pig. 
Six experiments of this, kind were performed by me (Expts. 4-9). 
In two of these the pigs undoubtedly suffered from Ascaris pneumonia 
(Expts. 6 and 8). In one there was also some evidence of this condition 
(Expt. 7). The culture used on two of the remaining three was proved 
active on mice (Expts. 4 and 5), while in the remaining case four different 
cultures were employed, the eggs in each containing active- embryos 
(Expt. 9). 
Results. In four of these animals (Expts. 4, 5, 8, 9) no worms were 
found in the intestine on section (with the exception of Expt. 8, in which 
one small Ascaris was found which was certainly not connected with 
the experiment performed several months previously). In one (Expt. 6) 
although a large number of worms were found it is probable that they 
did not originate in the experiment. In one (Expt. 7) a number of 
worms were found which may have originated in the experiment, but 
which may also have arisen from accidental infection. Comparing 
the measurements of the worms in Expts. 6 and 7, and the period 
which elapsed between the administration of the eggs and the finding 
of the worms in the two cases it is clearly not possible that the worms 
in both Expts. 6 and 7 originated from the eggs that were given. Out 
of the six experiments therefore five are negative, and one only possibly 
positive. Considering the very large number of larvae which must 
have reached the intestine, more than a thousand in each case, and the 
regularity and certainty with which the hepatic-pulmonary infection 
follows the administration of eggs in both the rat, mouse and pig, the 
evidence of these six experiments is opposed to the hypothesis of direct 
development without an intermediate host. Nevertheless six experi¬ 
ments are not sufficient to decide the matter and it must therefore still 
be considered unsolved. 
