276 EXPERIMENT STATION RECORD. [Vol. 43 



"If Ascaris eggs containing fully developed embryos are swallowed by rais>, 

 mice, guinea pigs, or rabbits, tbey hatch in the small intestine. Some of the 

 newly hatched larvjne may be eliminated in the feces, but others penetrate the ' 

 wall of the alimentary tract and, apparently aided by the circulation, mi- 

 grate to the liver and lungs ; they may also migrate 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 

 larvjK undergo growth and development, reaching 5 to 10 times their original 

 length before leaving the lungs, after which no material change occurs in 

 size or structure. Larvae that do not reach the lungs ultimately die and be- 

 come encysted or absorbed by the surrounding tissues. From the lungs the 

 larvae crawd up the trachea, then down the esophagus, through the stomach, 

 into the intestine, and finally pass out of the body in the feces. They may 

 be found in the liver as eai'ly as 2 days after infection, in the lungs and 

 trachea as early as 3 days after infection, and in the alimentary ti-act after 

 their passage through the lungs as early as 6 days after infection. They are 

 common in the lungs a week to 10 days after infection, becoming scarce in 

 the liver as they become numerous in the lungs. Within a little over two 

 weeks after infection all or practically all the larvae are usually eliminated, 

 but have been found still present and active in the liver, lungs, and alimentary 

 tract as late as 23 days after infection. 



" In young goats and lambs the larvre of A. siiutn, after migrating through 

 the lungs, settle down in the small intestine and undergo development ap- 

 proaching maturity, these animals thus being better adapted as hosts than 

 rats, mice, guinea pigs, and rabbits. In pigs Ascaris larvae, after migrating 

 through the lungs, settle down in the small intestines and develop to ma- 

 turity, and presumably the same cycle occurs in human beings. Rats and 

 mice play no part in the normal life history of Ascaris. The behavior of the 

 larvae in these animals and in guinea pigs and rabbits may be considered sim- 

 ply an expres.sion of imperfect adaptation of the parasites to existence in 

 these hosts. In pigs and human beings Ascaris may develop to maturity 

 within two and -one-half months after infection. In guinea pigs the larvae 

 apparently reach a larger average size than in mice in the same length of time, 

 and still larger in rabbits. 



" Migrating Ascaris larvae produce destructive lesions in the liver and lungs, 

 especially in the latter. Some larvae die during their migrations. Dead and 

 degenerated larvae have been found in the lungs as late as 86 days after infec- 

 tion, and in the liver 296 days after infection. The invasion of the lungs by 

 Ascaris larvae may result in a serious and sometimes fatal pneumonia, which 

 appears in a week to 10 days after ingestion of the eggs. 



" Young pigs are more susceptible to Ascaris infection than older animals, 

 but may not entirely lo.se their susceptibility with advancing age. No evidence 

 has been obtained that one infection with Ascaris renders animals less sus- 

 ceptible to later infections. If properly Incubated Ascaris eggs are injected 

 beneath the skin they will hatch, and the larvae will migrate to the lungs, 

 where they may be found a few days after injection of the eggs to have reached 

 the same stage of development as they w^ould if infection had occurred from 

 swallowing the eggs. The larvae of Belascaris marfi'mata undergo migrations 

 in rats similar to those of A. suum and A. Uimbricoides. 



" Immature stages of a nematode resembling and probably identical with 

 A. anoura have been found in the lungs of a python, indicating that this species, 

 like A. Umihricoides and B. marginata, migrates through the lungs, reaching, 

 however, a more advanced development before moving into the alimentary 



