Volume X 
JANUARY, 1918 
No. 2 
ON THE DEVELOPMENT OF ASCARIS LUMBRI- 
COIDES AND A. MYSTAX IN THE MOUSE. 
PART II. 
By F. H. STEWART, M.A., D.Sc., M.B., Major I.M.S. 
(With. Plate IV.) 
In previous papers 1 the migration of Ascaris lumbricoides in the 
rat and mouse has been traced to the point at which the larvae of the 
worm reach the trachea of these animals on the 8th day after infection. 
As the result of further experiments it is now possible to trace the 
migration through a further stage, namely that occurring from the 
9th to the 15th days after infection. My experiments have not as yet 
been carried beyond the 15th day and in the following summary the 
statement that larvae occur in a given situation up to the 15th day is 
not intended to imply that they do not persist therein after that date. 
Larvae are found in the mouths of infected mice on the 8th day, 
on which day they are also, as previously stated, abundant in the lungs 
and trachea. They persist in the lungs up to the 15th day. On the 
9th day they begin to travel down the alimentary canal and may be 
found in small numbers in the stomach, small intestine and caecum. 
On the 10th day this stage is fully established, the larvae travel with 
some rapidity through the stomach and small intestine and accumulate 
in the caecum and upper colon where as many as 60-70 may occur. 
On this day they also commence to pass out in the faeces. The passage 
from the lungs to the caecum continues up to the 15th day and larvae 
occur in the faeces on the 16th day. 
Between the 9th and 15th days the larvae increase in length. They 
measure from 1-3-2 mm. on the 10th day and 1-75-2-37 mm. on the 15th. 
1 Brit. Med. Journ. (July 1st and Oct. 7th, 1916); Parasitology (Feb. 26th, 1917), 
ix. 213-227, PI. I. and 9 text-figs. The subject dealt with in the present paper has 
already been partly described in the Brit. Med. Journ. Dec. 2nd, 1916. 
Parasitology x 
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