f 
LIFE HISTORY OF ASCARIS LUMBRICOIDES. 3 
to 1.45 mm. in length, and in a rabbit 8 days after infection from 0.99 
to 1.33 mm. in length. 
Migrating Ascaris larve pass from the esophagus through the 
stomach into the small intestine. We have observed them in the 
stomach of a guinea pig 7 days, and of rabbits 8 and 10 days, after 
feeding with A. suum eggs. Numerous larvee were present in the 
first and fourth stomachs of a kid that died 27 days after a first 
feeding and 10 days after a second feeding with Ascaris swum eggs. 
The shortest time after infection for the return of migrating Ascaris 
larvee to the small intestine that we have observed has been 6 days. 
In a guinea pig a few larve were observed in the small intestine 6 
days after Ascaris suum eggs had been fed. In the rabbit they have 
been found in the small intestine as early as 8 days, and in the 
mouse as early as 9 days after infection. In a mouse fed Ascaris 
suum eggs 10 days before, larvee were found in the small intestine 
measuring from 0.83 to 1 mm. in length. In mice the larve have 
been observed to persist in the small intestine as late as 23 days after 
infection. In rats, mice, guinea pigs, and rabbits the larve continue 
_ their migrations down the alimentary tract and pass into the large 
intestine. They can be found commonly without difficulty in the 
cecum during a certain period. We have seen them in this location 
in mice as early as 9 days and as late as 23 days after infection. 
Those seen on the ninth day measured 0.38 to 0:46 mm. in length; 
larvee measuring 0.75 to 1.45 mm. were present in the cecum of a 
mouse 10 days after infection. Stewart (1916c) found the larve 
in the large intestine of mice 9 to 12 days after they had been fed 
the eggs of Ascaris suum. He also found them in the feces of mice 
as early as 9 days and as late as 12 days after infection, and in the 
feces of a pig Stewart (1918b) found dead larve 11 days after 
infection. We have observed them in the feces of the mouse as late 
as 13 days after infection, their length ranging from 1.2 to 1.75 mm. 
Summarizing the observations that have been made on the migra- 
tions of Ascaris larve in rats, mice, guinea pigs, and rabbits, it may 
be stated that they can be found in the liver as early as 2 days after 
infection, in the lungs and trachea as early as 3 days after infection, 
in the esophagus and small intestine as early as 6 days after infec- 
tion, and in the large intestine and in the feces as early as 9 days 
after infection. They may still be present in the liver, lungs, and 
alimentary tract 23 days after infection, but, as first pointed out by 
Stewart, rats and mice usually become free from the parasites in a 
little more than 2 weeks after infection, and we have found the 
same to be true also of guinea pigs and rabbits. 
Ascaris infestation in rats, mice, guinea pigs, and rabbits accord- 
ingly persists only 2 or 3 weeks. After the first elimination of un- 
hatched eggs and newly hatched larve in the feces that takes place 
