8 BULLETIN 817^ U. S. DEPT. OF AGKICULTUEE. 



the lungs, reaching the same stage of development as they would 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 with 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 through the 

 skin, the hatching of Ascaris eggs when injected subcutaneously and 

 the prompt migration of the larvse 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 larvse 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 experiment 

 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- 



