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 bronchj, 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 larvse 

 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 

 rhinaria, the larval 

 tongueworm from 

 the liver and lymph 

 glands of cattle, 

 sheep, etc. En- 

 larged ten times 

 (after Rallliet), 



Fleas. — In the western United States investiga- 

 tions indicate that the commonest flea attacking 

 man is the so-called human flea, Pulex irriians, 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, 

 Gtenocephalus cards (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 



