THE DOG AS A CARRIER OF PARASITES AND DISEASE. 
19 
the walls of the intestine and encysts in the lungs, liver, kidney, 
lymphatic glands, etc., where it develops to the larval stage (fig. 11). 
Subsequently they break out of their cysts and resume their migra- 
tions, wandering through the tissues, causing more or less damage, 
until they reach the abdominal or thoracic cavity, sometimes enter- 
ing the intestines and bronchi, and at times causing the death of the 
host. Just how they get from here to the nasal passages of the dog 
is not very well known, though it is certain that this takes place. 
Possibly larvae are at times sniffed up by the dogs as they nose 
through an infested carcass; possibly in eating such a carcass larvae 
pass directly from the mouth of the dog back to the posterior por- 
tion of the nostril by way of the pharynx, or the parasite may re- 
turn from the stomach by way of the esophagus. The adult worm 
has been reported, but very rarely, from the nasal 
passages of man. 
The larvae are apt to be overlooked in necropsies 
on the human cadaver, but have been recorded in 
as high as 25 per cent of necropsies, In various 
localities in Germany they are commonly present 
in 3 to 4 per cent. This is a widely distributed 
parasite, and is found from time to time in the 
United States. A case in man has been recorded 
from the Canal Zone. 
Prevention consists in keeping viscera of ani- 
mals away from dogs, unless the viscera are cooked, 
and in a reasonable attention to what a dog eats, 
and this involves a responsible supervision of the 
dog's wanderings and conduct in all respects. 
FLEAS AND TICKS. 
Fig. 11. — Linguatula 
rliinaria, the larval 
tongueworm from 
the liver and lymph 
glands of cattle, 
sheep, etc. En- 
larged ten times 
(after Railliet). 
Fleas. — In the western United States investiga- 
tions indicate that the commonest flea attacking 
man is the so-called human flea, Pulex irritans, of which man is the 
primary host. The same investigations indicate that the dog is a 
most important carrier of that flea, probably the most important. 
Of 456 fleas collected from dogs in Berkeley, Cal., 29 per cent were 
of this species. In the eastern United States investigations indicate 
that the commonest flea attacking man is the so-called dog flea, 
Ctenocephalus cams (fig. 12), and here, of course, the dog is the 
normal host and the usual carrier. 
Either species of flea constitutes an annoying pest. The bite is 
distinctly unpleasant and in the summer nights may prove just the 
