LIFE HISTORY OF ASCARTS LUMBRICOIDES. 11 



feeding- Ascaris suum eggs. Apparently they leave the liver more, 

 rapidly in the case of guinea pigs and rabbits than in the case of 

 mice, though this may be only apparent. Given the same number of 

 larvae in the small liver of a mouse and in the relatively large liver of 

 a guinea pig or rabbit, the presence of larvai in the former case might 

 be easily detected, and in the latter only with difficulty or not at all. 

 We have actually never seen them in the liver of a guinea pig. Most 

 of our guinea pigs, however, were killed or died later than 4 days 

 after feeding. Rabbits that were killed or died 8, 10, 86, and 99 days 

 after feeding Ascaris suuni eggs showed no larvae in the liver. Rab- 

 bits killed 3 and 5 days after feeding showed numerous larvae in the 

 liver, 0.2 to 0.25 mm. long in tlie first case and 0.23 to 0.45 nun. long 

 in the second. 



With reference to the path of migration from the intestine to the 

 liver and thence to the lungs, it has been pointed out (Stewart, 1917a, 

 p. 227) that there are two apparently possible ways in which the 

 larva? can get from the intestine to the liver and later to the lungs. 

 Assuming that inasmuch as the thickness of the newly hatched larva 

 is three times the diameter of a red blood corpuscle of the mouse, it 

 can not pass through the lumen of an ordinary capillary vessel. 

 (1) The larva enters a mesenteric venule and is carried to the liver, 

 where it is arrested at the entrance to the hepatic capillary plexus. 

 Acute fatty degeneration of the liver tissue enables the larva to pene- 

 trate along the capillaries between the degenerated columns of the 

 liver cells to the hepatic venules. The larva then passes in the 

 hepatic vein and vena cava to the heart, and by the pulmonary ar-tery 

 to the lung. There it is arrested by the pulmonary capillaries. Hem- 

 orrhages of the arterioles result and the larva penetrates into the 

 air vesicles. (2) The newly hatched larva travels up the bile duct 

 and reaches the bile capillaries of the interlobular zone. Working 

 its way through the degenerated liver tissue, it reaches a hepatic 

 venule and continues its course as in the first case. 



Observations made by the writers are in hannony with the sugges- 

 tion that migration from the intestine to the liver may be by way 

 of the portal system, and from the heart to the lung by the pul- 

 monary artery. Owing to the difficulty of avoiding possible con- 

 tamination with larvae from other locations than the vessels from 

 which the blood was taken in our experiments (Nos. 11 and 12), the 

 results of the experiments should not be accepted as in themselves 

 sufficient proof of the migration of the larvae in the path indicated. 

 From general considerations, however, Stewart's first suggestion 

 seems more likely to be correct than the alternative suggestion. As 

 noted elsewhere, it is quite probable that some larvae migrate along a 

 route different from either of those suggested by Stewart. 



