104 THE FUR SEALS OF THE PRIBILOF ISLANDS. 



Worms of this genus occur in the adult stage in the stomach and intestine of various 

 animals. They are occasionally reported in other poi'tions of the body, as the mouth, 

 nasal passages, bile ducts, peritoneal cavity, etc. In many instances this aberrant 

 position of the worms is undoubtedly due to an active wandering of the parasites after 

 the death of the host, although cases are also recorded where the nematodes ha\'e been 

 taken from other portions of the body than the stomach and intestine immediately 

 after death. Cases are aUo recorded of expulsion of ascarides through the mouth 

 or nose during the life of the host. 



A few ascarides may occur in an animal and yet not have any serious eft'ect upon 

 it, especially if the host is large. When present in considerable numbers, however, 

 they are undoubtedly of importance and may bring about serious trouble. The injury 

 to the host may be of different kinds: 



(1) By the i»resence of a large number of ascarides the lumen of the intestine may 

 be so tilled as to cause a temporaiy stojipage of the bowels. 



(2) A wandering of ascarides from the intestine to the liver tlirougli the bile 

 ducts, which rarely occurs, may interfere with the flow of the bile, and may even result 

 in more serious complications. 



(3) It is claimed by some that the ascarides may perforate the intestine, especially 

 in case of intestinal ulceration, and thus gain access to the body cavity. An ingress 

 of faecal matter through the perforation will result in peritonitis and thus lead to 

 death. Such active perforation of the intestinal wall is, however, certainly rare. 



(4) The assimilation of food by the ascarides results of course in depriving their 

 hosts of a (certain «iuantity of nourishment; but this will be iusigniticant in cases of 

 light infections. 



(5) Some ascarides have very strong lips and become firmly attached to the Avails 

 of the intestinal tract. It is but natural that numerous wounds in the mucosa arising 

 from the lips and teeth of the worms should produce some injury, as they would form 

 points of attack for bacteria. If Murie's opinion (see p. 139) is correct that the ulcers 

 in the stomach of the walrus he examined were due to the presence of the ascarides 

 found, these ulcers probably began in this way. 



(G) It has been sliowu that some ascarides secrete a substance which produces a 

 swelling around the eyes, a profuse flow of tears, and intense itching. This action 

 on the part of the ascarides of seals does not seem to have been noticed as yet. 



The above-known conditions are taken from ascaride infection of hmd animals. 

 We know nothing of the effects of these parasites upon the seals; but we do not 

 hesitate to assume from analogy that they will have practically the same effect upon 

 seals which similar parasites have ui)ou other animals. We do not, however, believe 

 that they will enter .into serious consideration in connection with the mortality of 

 seals, since death from ascarid infection must be exceedingly rare. 



It is generally assumed that ascarides are all autoecious i^arasites; that is, they 

 have a direct development with only one host. While this point has been established 

 for A, lumhricoides of man, it will be shown below that seals become infested by eating 

 fish. 



This fact has an important bearing upon the relation of these worms to the 

 diseases of the seals, for although we may lind ascarides in very young dogs and cats, 

 the pups of seals will not become infected with them until they begin to eat fish. In 

 other words, while the crowding on the rookeries would naturally present conditions 



