44 
Ascaris lumbricoides 
V. The route taken by the larvae of A. Suilla Duj. in their 
MIGRATION THROUGH THE TISSUES OF THE HOST. 
The larvae of Ascaris lumbricoides and its relations live actually within 
the tissues of their hosts from the moment they perforate the walls of the 
intestine (assuming they do not ascend the bile ducts) until they reach the 
alveolar spaces of the lungs. Theoretically considered they could travel from 
the intestine to the lung along two paths, namely (1) bv the veins and pul¬ 
monary artery, and (2) by the lymphatics and blood-vessels, and (3) by a 
third method directly through all intervening tissues, availing themselves 
only incidentally of such natural spaces as they encountered on the line which 
they happened to take. 
The first is that which I suggested (Stewart, 1917, p. 226). It has been 
accepted with reservations by Ransom and Foster. It is the route followed by 
a minority of the larvae of Agchylostoma. The second is that followed by the 
majority of the Ankylostome larvae. Larvae coming from the small intestine 
would by this route traverse the lacteals, cysterna chyli, and thoracic duct to the 
left subclavian vein. The third route has been suggested recently by Yoshida. 
“It is believed that the larvae migrate in every direction boring through 
various organs or tissues by means of their own power of piercing but not by 
way of blood-vessels.' 5 “The general and important course of migration by 
the ascarid larvae in the body of the host may be as follows: The ascarid 
larvae proceed to the abdominal cavity by boring through the wall of the 
intestine. Thence they pierce the diaphragm to enter the pleural cavity, finally 
penetrating into the lungs from their surface, ft might be considered as an 
additional and mere accidental course of migration that the larvae in the 
abdominal cavity penetrate into the liver, thence they are carried to the lungs 
by the way of blood-vessels, passing through the heart.” 
Yoshida advances the following arguments in favour of his hypothesis. 
(1) That he has found larvae in the abdominal cavity in large numbers during 
the first 48 hours, in lesser numbers thereafter. He has also found them in 
the pleural cavities and in organs lying off the direct blood route, viz. spleen, 
kidney, and pancreas. He also states that histological study shows “that 
almost all the larvae in the lungs and liver are not found in the blood vessels, 
but in other tissues.” His infection experiments prove that the larvae can 
migrate from the serous cavities to the lungs. 
The following considerations are opposed to this view: (1) In Yoshida's 
own experiments the liver was apparently found to contain as many larvae 
as the abdominal cavity during the first 48 hours. I have examined the 
pleural and abdominal cavities during the first 48 hours in three cases only, 
v T hich of course do not permit of a conclusion, especially in view of Yoshida’s 
very definite results, but I have failed to find larvae in these cavities, although 
they were present in the liver. (2) My experience of serial sections differs 
entirely from that of Yoshida. I have found that the majority of larvae in the 
