12 BULLETIIT 81*7, 17. S. DEPT. OF AGRICULTTJKE. 



Stewart (1916a) found larvse in the lungs of a mouse within 4 

 da^'s after it had been fed Ascaris lumbricoides eggs. We have found 

 larvse in the lungs of the rabbit and guinea pig as early as 3 days 

 after feeding Ascaris suum eggs. In rats, mice, guinea pigs, and 

 rabbits they may be found commonly in the lungs in large nmnbers 

 from 4 to 6 days after infection. As they become numerous in the 

 lungs they disappear from or become scarce in the liver. In size the 

 larvse observed by us in the lungs varied in length from 0.2 or 0.3 

 mm. (that is, the same as the newly hatched larva), up to 1.8 mm. 

 Larvee of the latter length have been observed in the lungs of rabbits 

 10 days after infection, and slightly smaller in the lungs of a mouse 



13 days after infection. There is considerable variation in the size 

 of larvse found in the lungs at the same time. For example, larvse 

 varying in length from 0.29 to 0.6 mm. were observed in the lungs of 

 a mouse 7 days after infection; in a.nother mouse from 0.6 to 1.12 

 mm. 10 days after infection; in a guinea pig from 0.3 to 0.45 mm. 4 

 days after infection; in another guinea pig 0.35 to 0.83 mm. 5 days 

 after infection; in another guinea pig 0.63 to 0.93 mm. 6 days after 

 infection; in a rabbit from 0.23 to 0.48 mm. 5 days after infection; 

 and in another rabbit 0.9 to 1.8 mm. 10 days after infection. We 

 have observed that living larvse may still be found in the lungs of a 

 mouse as .late as 23 days after infection, and we have found dead 

 larvse encapsulated in the lungs of a rabbit killed 86 days after infec- 

 tion, and in the lungs of a pig we have observed degenerated larvse 

 65 days after infection. 



The larvse in the lungs (Stewart, 1916a) enter the air vesicles and 

 wander into the trachea. He found them in the bronchi as early 

 as the seventh day and in the trachea as early as the eighth day after 

 infection. We have found a larva in the trachea of a rabbit 3 

 days, and in the trachea of a guinea pig 5 days, after infection. 

 They are often numerous in the trachea 6 days after infection. The 

 smallest observed in the trachea was 0.23 mm. long (rabbit, 3 days 

 after infection). In a pig 7 days after infection larvse were observed 

 in the trachea, varying from 0.67 to 1.33 mm. 



From the trachea the larvse enter the pharynx. We have recovered 

 larvse from the mouth of an experimentally infected animal. 



From the pharynx the larvse pass down the esophagus. They have 

 been observed in the esophagus as early as 6 days after infection 

 (guinea pig, rabbit). The latest we have observed them in the 

 esophagus has been 10 days after infection (rabbit). No doubt they 

 may be found still later. In a pig, 9 days after infection, we have 

 observed- larvse in the esophagus, and there were numerous larvse 

 in the esophagus of a kid that died 27 days after a first feeding and 

 10 days after a second feeding with Ascar-is suum eggs. In a mouse 

 9 days after infection the larvse in the esophagus varied from 0.9 



