8 BULLETIN 817, U. S. DEPT. OF AGRICULTURE. 
the lungs, reaching the same stage of development as they would i in 
a similar time if the eggs had been swallowed. 
Under natural conditions there appears to be little likelihood of 
infection through the skin. As noted elsewhere in this article, 
Ascaris eggs sometimes hatch outside the body, but it is not known 
whether the newly hatched larva can penetrate the uninjured skin. 
The fact that the hatching of the eggs outside the body is a rela- 
tively rare occurrence indicates that infection through the skin, if 
it occurs at all, is likely to be very unusual. Possibly, however, eggs 
in contact mails the skin on some parts of the body may hatch much 
more commonly than they do away from the body. Other possibili- 
ties can also be imagined, such as the introduction of the eggs into 
wounds and into the vagina. 
Apart from the question of the possibility of infection thr ough the 
skin, the hatching of Ascaris eggs when injected subcutaneously and 
the prompt migration of the larve to the lungs are of interest as 
demonstrating that the action of the digestive juices is unnecessary 
for the hatching of the eggs, and that the larve are probably aided 
by the circulation in their migration to the lungs. 
HATCHING OF ASCARIS EGGS. 
When Ascaris eggs containing fully developed embryos are swal- 
lowed they pass through the stomach unhatched; at least the great 
majority do. In view of the occasional hatching of Ascaris eggs out- 
side the body in various media it is evidently possible that hatching 
in the stomach may sometimes occur. In fact, Martin (1913) ob- 
served empty eggshells and free embryos in the stomach contents 
of a rat and a mouse fed Ascaris eggs experimentally. The egg- 
shells, however, were irregularly torn and all the embryos were 
dead. Martin believes that the apparently hatched eggs seen by 
him in the stomachs of experimental animals were eggs that had 
been crushed by the teeth of the animals in chewing the material 
with which the eggs were fed. In any event it appears quite cer- 
tain that hatching in the stomach is not a normal occurrence. 
Davaine (1863) fed a large number of eggs of A. lumbricoides 
containing fully developed embryos to a rat which was killed 12 
hours later. In the small intestine he found unhatched eggs, eggs 
in the process of hatching, and free embryos. In another eean 
a rat was fed large numbers of Ascaris eggs and numerous active 
embryos were afterwards observed in the feces as well as unhatched 
eggs, and eggs in the process of hatching. Davaine also placed 
Ascaris eggs in small glass tubes closed at the ends with gauze and 
fed them to a dog. These were recovered in the feces 2 days later. 
The eggs in early stages of segmentation were unchanged, free em- 
