LIFE HISTORY OV ASCARTS LUMBRICOIDES. 13 



to 1.45 mm. in Itnigth, and in a rabbit 8 days after infection from O.IM) 

 to l.;{;^ nnn. in length. 



Migrating Asoarl^ larvae pass from tlie esophagus through tho 

 stomach into the small intestine. We have observed them in the 

 stomach of a guinea pig 7 days, and of rabbits 8 and 10 days, after 

 feeding with A. sumn eggs. Numerous lai'va? were present in the 

 first and fourth stomachs of a kid that died 27 days after a first 

 feeding and 10 days after a second feeding with Ascmis suimi eggs. 

 The shortest time after infection for the return of migrating Ascaris 

 larva^ to the small intestine that Ave liave observed has been 6 days. 

 In a guinea pig a few larvae were observed in the small intestine (J 

 days after Ascaris suunn eggs had been fed. In the rabbit they have 

 been found in the small intestine as early as 8 days, and in the 

 mouse as early as 9 days after infection. In a mouse fed Ascaris 

 suum eggs 10 days be;fore, larvae were found in the small intestine 

 measuring from 0.83 to 1 mm. in length. In mice the larvae have 

 been observed to persist in the small intestine as late as 23 days after 

 infection. In rats, mice, guinea pigs, and rabbits the larvae continue 

 their migrations down the alimentary tract and pass into the large 

 intestine. They can be found commonly without difficulty in the 

 cecum during a certain period. We have seen them in this location 

 in mice as early as 9 days and as late as 23 days after infection. 

 Those seen on the ninth day measured 0.38 to 0.46 mm. in length; 

 larvae measuring 0.75 to 1.45 mm. were present in the cecum of a 

 mouse 10 days after infection. Stewart (1916c) found the larvae 

 in the large intestine of mice 9 to 12 days after they had been fed 

 the eggs of Ascaris suum. He also found them in the feces of mice 

 as early as 9 days and as late as 12 days after infection, and in the 

 feces of a pig Stewart (1918b) found dead larvae 11 days after 

 infection. We have observed them in the feces of the mouse as late 

 as 13 days after infection, their length ranging from 1.2 to 1.75 mm. 



Summarizing the observations that have been made on the migra- 

 tions of Ascaris larvae in rats, mice, guinea pigs, and rabbits, it may 

 be stated that they can be found in the liver as early as 2 days after 

 infection, in the lungs and trachea as early as 3 days after infection, 

 in the esophagus and small intestine as early as 6 days after infec- 

 tion, and in the large intestine and in the feces as early as 9 days 

 after infection. They may still be present in the liver, lungs, and 

 alimentary tract 23 days after infection, but, as first pointed out by 

 Stewart, rats and mice usually become free from the parasites in a 

 little more than 2 weeks after infection, arid we have found the 

 same to be true also of guinea pigs and rabbits. 



Ascaris infestation in rats, mice, guinea pigs, and rabbits accord- 

 ingly persists only 2 or 3 weeks. After the first elimination of un- 

 hatched eggs and newly hatched larvae in the feces that takes place 



