MUCOUS COAT OF THE DIGESTIVE CANAL. 
461 
carnivora. I have never seen them in the dog, although I have 
carefully examined the stomach of that animal, in cases of 
poison, and of hemorrhage, both from the stomach and the 
intestines. 
Of the omnivora, I can only say that I have examined the 
digestive passages of some young pigs, and have not found any 
worms. 
I do not know whether these hairs are natural to the digestive 
passages of the human being. I am inclined to think that they 
are. They have occasionally been seen, but they have hitherto 
been regarded as anomalies. The skin of the human being is 
but slightly furnished with hair, and therefore it would probably 
exist in a proportionably small quantity in the digestive canal, 
and would be generally overlooked, or, perhaps, except under 
peculiar circumstances, be rarely visible. 
I have in vain searched for hairs in the horse, the ox, the 
sheep, and the dog on the mucous membrane of the oesophagus, 
the pharynx, the larynx, the nasal passages, the trachea, the 
conjunctiva, and the genital passages: in neither of them have 
I found the least trace of such a production, and therefore I do 
not think that in a normal state it exists — still I have referred 
to facts which prove that they have accidentally been found on 
the conjunctiva of some animals, and, in a healthy state of the 
parts, they are always found on the caronele of the larger kinds 
of animals. 
But how is it that, though almost always found in the horse, 
it is only on certain parts of the alimentary canal ? This is 
an interesting inquiry, and, in order to give a satisfactory 
answer to it, it will be necessary to examine what is the state 
of the mucous surface on which they are found, and that on 
which they are wanting. 
In the right sac of the stomach, the small intestine, the 
caecum, and the curvatures of the colon, the mucous coat, more 
or less thick and organized, is covered only by a humour of little 
consistence, and that may be elevated and removed without 
much difficulty. On the contrary, in other parts of the diges- 
tive tube, the same membrane is either covered by a thick epi- 
thelium, like the left sac of the stomach and the oesophagus, or 
with a thick and tough mucus, like the rectum and the float- 
ing portion of the colon. Then the presence of this thick and 
hard epithelium, explains, to a certain degree, the absence of 
the hair, and so likewise do the thick and tough mucosities in 
a portion of the colon and of the rectum. 
What is the use of these hairs ? All that can be said on this 
point must be purely theoretical. They are found only where 
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