226 
Development of Ascaris 
after infection. Dead larvae have been found in the stomach and 
rectum on the ninth day after the last infection. 
The route by which the larvae reach these sites is of course not 
definitely proved but from anatomical considerations it is hardly 
possible that it can be other than one of the two following (the 
diameter of the larva is three times that of a red blood corpuscle of the 
mouse. The larva could therefore not pass through the lumen of an 
ordinary capillary vessel); 
(1) Boring through the wall of the stomach or intestine the larva 
enters a mesenteric venule and is carried to the liver. It is here arrested 
at the entrance to the hepatic capillary plexus and it is for this reason 
that so many larvae are found in the capillaries close to the interlobular 
veins. The liver undergoes extreme and acute fatty degeneration so 
that the larvae are able to penetrate along the capillaries between 
the degenerated columns of liver cells to the hepatic venules. Thence 
they pass in the hepatic vein to the heart and by the pulmonary artery 
to the lung. They are of course at once arrested by the pulmonary 
capillary field. Embohsm of the smaller branches of the pulmonary 
artery takes place with haemorrhage around these arterioles. The 
larvae readily work their way along with the effused blood into the air 
vesicles and thence into the bronchi and trachea. 
(2) The larva after hatching in the stomach or duodenum travels 
up the bile duct and reaches the bile capillaries of the interlobular 
zone. It here bores its way through the degenerated liver tissues 
and reaching a hepatic venule continues its course as in the first case. 
During the residence in the body of the rat or mouse the larvae 
grow from a length of 0-22 mm. to 1-4 mm. The proportion length 
of oesophagus/total length diminishes from 1/2-5 to 1/6-1. The ventral 
line which is the greatest of the longitudinal lines in the embryo is 
reduced to the same dimensions as the dorsal and lateral lines. The 
ventral gland (the rudiment of the excretory system) is developed from 
a cell of the ventral line, enlarges very greatly, acquires the massive 
nucleus characteristic of Ascaris larvae (Stewart, 1906; Bayhs, 1916) 
and finally develops its duct from the cells of the ventral line. The 
intestine, anal canal and anus become pervious. The rudiment of the 
female gonads appears. 
