DIGESTIVE ORGANS AND THEIR ANATOMY. 265 



jected directly into the blood-vessels, and is not utilized at 

 all as nourishment. 



Then again, the vitality of the tissues depends largely 

 upon the constancy and permanency of the blood supply, 

 and to place at once into the blood stream varying quanti- 

 ties and diverse kinds of foods would react at once, and ma- 

 terially interfere with the normal and continued activity of 

 the cells. To transform foods and change them into sub- 

 stances which may be carried by the blood and utilized by 

 the tissues, there is provided by the body one of the most 

 extensive and complicated systems, familiarly termed the 

 alimentary system or digestive apparatus. Before noticing 

 how the foods are affected and in what manner they are pre- 

 pared for the blood, it is necessary to become acquainted 

 with the anatomy of this system itself. 



THE MOUTH. 



' The mouth serves as the entrance place for not only the 

 solid and liquid foods, but also for the gaseous food, the 

 oxygen of the air, a food in no less sense than bread and 

 butter. However, in the mouth the solid and liquid foods 

 are carried to the pharynx and gullet and into the stomach, 

 while the gaseous food in the manner already described, is 

 carried to the lungs. The lung is in no far-fetched sense, 

 then, an adjunct of the alimentary canal, intended to digest 

 that food which, on account of its gaseous condition, does 

 not need the action of further juices to prepare it for ab- 

 sorption. Leading out of the mouth are six openings: The 

 two posterior nares, connected with the nose and serving as 

 passage-ways for the air ; two Eustachian tubes leading from 

 the back of the mouth to the ear, and to be described 

 further in the chapter on hearing; the pharynx, leading into 

 the gullet, and in front of the pharynx, the larynx, or voice- 

 box leading to the trachea. While the mouth, tongue and 

 teeth figure in an integral way in the formation of speech, 

 we are concerned here only with their digestive function. 



This is mainly the process of mastication, made possible by 



