LIFE HISTORY OF ASCAEIS LUMBRICOIDES. 9 



bryos were found in the tu'oes, hut egp:H contuining active embryos 

 were no longer present. As Davuine in his experiments never found 

 eggs hatching in the stomach, and only in the intestine, he concluded 

 that hatching does not occur imtil after the eggs have passed to the 

 small intestine. It was also shown by Davaine that some of the 

 newl}^ hatched larva3 may pass out of the body in the feces, and he 

 supposed that this regularly occurs if the animal that has ingested 

 the eggs 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 Iwnibnooides 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 Ascwis eggs. Martin (1913) like- 

 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. T\niat 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 breakthrough it. 

 Martin (1913) reaches the following conclusions: 



Hatching depends upon three factors : First, complete development of tlie em- 

 bryo ; second, a surrounding medium that is alkaline or neutral in reaction ; ana 

 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 suwn 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 

 Ascans eggs are yet to be determined. 

 . 137550"— 20— Bull. 817 2 



