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LIFE HISTORY OF ASCARIS LUMBRICOIDES. 15 
that the larve of Ascaris migrate actively through the tissues to the 
lungs after hatching in the intestine, and he considers that the pos- 
sible carriage of the larvee in the circulation, if it does occur at all, 
is of secondary importance. He would also explain the presence of 
larvee in the spleen, kidneys, and various other locations in which he 
has found them in addition to the lungs and liver, as resulting from 
an active penetration of the larvee through the tissues unaided by the 
circulation. 
DEVELOPMENT IN THE INTESTINE. 
After reaching the small intestine following their migration 
through the lungs, Ascaris larve, if ina suitable host, settle down and 
develop to maturity. It appears, however, that some of them may 
pass on out of the intestine and perish, just as they do in the case 
of rats, mice, guinea pigs, and rabbits. Stewart (1918b) noted dead 
Ascaris larvee in the feces of a pig 11 days after feeding the eggs. 
Accordingly, even though the host is one in which the parasites can 
reach maturity, not every larva that succeeds in completing the 
cycle through the lungs is able to establish itself in the intestine. 
This would seem to be the probable explanation of the fact that 
pigs fed the eggs of Ascaris swum experimentally and afterwards 
showing evidence of lung invasion by the larvee, may, when killed 
after a lapse of time sufficient for the development of the parasites 
to maturity or to a stage approaching maturity in the intestine, be 
found to harbor only a few worms or none at all. Such failures 
have been noted by us. For example, a pig 27 days old was fed 
numerous eggs of Ascaris suum, October 4, 1917. Another lot of 
eggs was fed to this pig November 10. On November 17, or 44 days 
after the first feeding and 7 days after the second, the pig was killed. 
The lver and lungs showed numerous petechiz similar to those 
occurring in other experiment animals in association with the in- 
vasion of these organs by Ascaris larvee, but no larvee were seen in 
the preparations examined. In the small intestine there were 8 
immature Ascaris, 5 of which were measured and found to range 
from 60 to 88 mm. in length. Another pig, from the same 
litter, that was fed Ascaris swum eggs September 22, when 15 days 
old, died 7 days later and showed numerous larvee in the lungs, 
trachea, and pharynx, those in the trachea ranging in length from 
0.67 to 1.338 mm. (Experiment No. 19). 
It is quite likely that the worms found in the intestine of the first 
pig came from the eggs fed 44 days before, but the result of the 
experiment by itself can not, of course, be considered conclusive 
proof that development of Ascaris in the intestines of pigs follows 
the ingestion of the eggs, nor that the larve which mature in the 
intestine first migrate to the lungs and back again before they settle 
