LIFE HISTORY OF ASCARIS LUMBRICOIDES. 43 



over 1 mm. Tliymus, spleen, and thyroid negative. Larvne in tracliea, jiliarynx, 

 and esophafjiis very abundant. Tracliea, pharynx, and esophagus show diffuse 

 inflammation of the mucous surfaces. Larvje numerous in first stomach and 

 iu fourth stomach, the latter showi-ns: 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 tlie eggs of Ascaris s-uum or A. Ivmbncoides in the 

 presence of oxygen and moisture may reach full development in 10 

 days if inculmted 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 e^gg is insoluble in many chemical reagents. 

 Within the shell there is a thin membrane which is Jiighly 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 embrj'o may occur accidentally outside the body 

 of a host, but occurs normally only in the small intestine. Hatching 

 also occurs if the egg is introduced beneath the skin. The factors 

 that govern the hatching of Ascaris eggs are yet to be determined. 

 Mai'tin's conclusions that hatching is caused by alkaline or even 

 neutral solutions acting at body temperature have not been confirmed. 



Ascmis 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. 



If Ascayi^s 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 larvae 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 larvse 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. Larvse that do not reach the lungs 

 ultimately die and become encysted or absorbed by the surrounding 

 tissues. From the lungs the larvse crawl up the trachea, then 

 down the esophagus through the stomach into the intestine, and 



