f 
LIFE HISTORY OF ASCARIS LUMBRICOIDES. 8) 
bryos were found in the tubes, but eggs containing active embryos 
were no longer present. As Davaine in his experiments never found 
eggs hatching in the stomach, and only in the intestine, he concluded 
that hatching does not occur until after the eggs have passed to the 
small intestine. It was also shown by Davaine that some of the 
newly hatched larvae may pass out of the body in the feces, and he 
supposed that this regularly occurs if the animal that has ingested 
the eges is one in which the parasites can not attain their complete 
development. 
By experiments in vitro Davaine (1858) found that the gastric 
juice of the rabbit and the dog will not digest the shell of the egg of 
Ascaris lumbricoides even when allowed to act 3 or 4 days. De Klug 
(1907) also observed that artificial gastric and tryptic digestion was 
without effect upon the shells of Ascaris eggs. Martin (1918) lke- 
wise found that various natural and artificial digestive juices do not 
dissolve the shells of Ascaris eggs. 
From the experiments and observations of Davaine, Martin, and 
others it would appear that the hatching of the egg is the result of 
efforts on the part of the contained embryo. The shell is split and 
the embryo emerges through the opening, pressing apart the edges of 
the opening as it emerges. What factor or factors determine hatch- 
ing is uncertain. Davaine (1859, 1863) reached the conclusion that 
the gastric juice does not act on the shell of the Ascaris egg and ex- 
pressed the opinion that although the intestinal juices do not dissolve 
the shell they soften it so that the embryo, stimulated to great activity 
by the temperature of the body of the host, is able to break through it. 
Martin (1913) reaches the following conclusions: 
Hatching depends upon three factors: First, complete development of the em- 
bryo; second, a surrounding medium that is alkaline or neutral in reaction ; and 
third, a temperature that is the same as the temperature of the host of the 
parasite. Digestive juices do not dissolve the eggshell. Hatching does not 
occur in the stomach, because of-its acidity; it does occur in the intestine be- 
cause of its alkalinity. 
In support of his conclusions as to the factors that determine hatch- 
ing, Martin has recorded the results of a considerable number of ex- 
periments in vitro with various media. The writers, in experiments 
on the eggs of Ascaris swum in vitro, have been unable to cause hatch- 
ing with any regularity. We have observed that a few eggs will 
hatch in vitro in almost any medium, including acid as well as neutral 
and alkaline media, not only at the temperature of the body but at 
lower temperatures. The vast majority of the eggs, however, do not 
hatch, although the contained embryos may remain alive and active. 
Apparently, therefore, the factors that influence the hatching of 
Ascaris eggs are yet to be determined. 
137550°—20—Bull. 817——2 
