ALIMENTARY CANAL. 3 



acquired by the lungs ; yet one thing is certain, that the body, 

 unless it be in very brief periods, must always lose more weight 

 by the lungs than it can gain. It is a sure truth, that by the 

 lungs the body can acquire nothing but oxygen, nitrogen, or 

 water. 



The name alimentary canal, or primce vice, is the term some- 

 what vaguely applied to the long passage including the gullet, 

 stomach, and intestines from the mouth to the fundament. 

 This canal has for its lining membrane a part of one of the 

 two great mucous membranes of the body, while another part 

 of the same great membrane descends through the windpipe, 

 lining its ramifications, and reaching to the very minute cavities 

 in which these terminate, called the air-cells of the lungs. 

 Another part of the same great membrane passes from the 

 back part of the throat to the tympanic cavity of the ear on 

 each side, and, rising upwards into the nostrils, extends through 

 the lachrymal passages to the fore part of the eyes and the inner 

 surfaces of the eyelids.* This vast extent of web is accounted 

 all one membrane, because its anatomical structure, though 

 considerably modified in certain parts, is everywhere of the 

 same general character, while it is continuous throughout that 

 is, through all this prolonged extent it shows no break or 

 interruption. It is called the gastro-pulmonary mucous mem- 

 brane, with reference to its two chief seats namely, the gastric 

 or alimentary passages, and the pulmonary or air passages. 

 The only other mucous membrane is quite detached from this, 

 being that which lines the urinary passages and the interior 

 >f the genital organs, this last is named the genito-urinary 

 mucous membrane, while it agrees in its general structure with 

 the gastro-pulmonary mucous membrane. 



To exclude for the present the genito-urinary mucous mem- 



* An explanation of the technical terms employed here and elsewhere in 

 the volume will be found in the Glossary at the end. 



