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LIFE HISTORY OF ASCARIS LUMBRICOIDES. 43 
over 1 mm. Thymus, spleen, and thyroid negative. Larve in trachea, pharynx, 
and esophagus very abundant. Trachea, pharynx, and esophagus show diffuse 
inflammation of the mucous surfaces. Larvee numerous in first stomach and 
in fourth stomach, the latter showing diffuse inflammation. The small intestine 
contained thousands of young ascarids varying in length from 4.3 to 11.4 mm., 
averaging 7.9 mm. (29 specimens measured). Presumably these latter were 
derived from the first feeding and are therefore 27 days old, while the smaller 
forms in the lungs, trachea, esophagus, and stomach are the result of the second 
feeding and are therefore 10 days old. 
GENERAL SUMMARY. 
~The embryos in the eggs of Ascaris suum or A. lumbricoides in the 
presence of oxygen and moisture may reach full development in 10 
days if incubated at a temperature of about 33° C., development pro- 
ceeding more slowly at lower temperatures and being inhibited by 
the lack of oxygen or moisture. 
The shell of the egg is insoluble in many chemical reagents. 
Within the shell there is a thin membrane which is highly imper- 
meable and even more resistant to solution than the shell itself. The 
shell may be dissolved with antiformin, leaving the embryo inclosed 
in the membrane, in which condition the embryo may continue active 
for several days. 
Hatching of the embryo may occur accidentally outside the body 
of a host, but occurs normally only in the small intestine. Hatching 
also occurs 1f the egg is introduced beneath the skin. The factors 
that govern the hatching of Ascaris eggs are yet to be determined. 
Martin’s conclusions that hatching is caused by alkaline or even 
neutral solutions acting at body temperature have not been confirmed. 
Ascaris eggs in large numbers may be conveniently obtained and 
developed to the infectious stage for experimental use by removing 
the eggs from the uteri of female worms and incubating them in a 
solution of formalin placed in shallow dishes and stirred every few 
days to insure sufficient aeration. 
Tf Ascaris eggs containing fully developed embryos are swallowed 
by rats, mice, guinea pigs, or rabbits they hatch in the small intestine. 
Some of the newly hatched larvee may be eliminated in the feces, but 
others penetrate the wall of the alimentary tract and apparently aided 
by the circulation migrate to the liver and lungs; they may also mi- 
grate to the spleen and thyroid and under the peritoneum of the 
abdominal cavity. Most of those entering the liver later migrate to 
the lungs. In the course of their migrations the larve undergo 
growth and development, reaching five to ten times their original 
length before leaving the lungs, after which no material change 
occurs in size or structure. Larve that do not reach the lungs 
ultimately die and become encysted or absorbed by the surrounding 
tissues. From the lungs the larve crawl up the trachea, then 
down the esophagus through the stomach into the intestine, and 
