42 PHYSIOLOGY AND HEALTH. 



The former alone is needed for, or can give nourishment 

 and strength to, the body. The latter is not only useless, 

 but a burden on the whole system, and must be regularly 

 excluded. Otherwise all the powers are oppressed, and 

 health suffers. 



76. The proportion of this chyle, which the absorbents are 

 able to extract from the chyme, varies with the food ; for one 

 kind contains a much greater ratio of nutriment than another, 

 as will be hereafter shown. It depends also upon the com- 

 pleteness of digestion in the stomach ; and this, in great 

 measure, upon the perfectness of the mastication and mixture 

 with saliva in the mouth. Of course, then, the remote 

 result of imperfect mastication and hasty eating mast be, 

 first, imperfect digestion ; second, less chyle ; and, conse- 

 quently, less nutriment for the body. 



77. Thus the work of digestion is shown to be performed 

 by means of the mouth, the stomach, and the alimentary 

 canal. The whole process is divided into three stages 

 mastication and insalivation in the mouth; the digestion, or 

 conversion into chyme in the stomach ; the separation of the 

 nutritious and innutritio'us parts in the duodenum. It is 

 necessary that each part should be well done, and in due 

 order ; else all that follow will be badly done.* 



* Dr. Dalton says, " We find, then, that the digestion of the food is not 

 a simple operation, but is made up of several different processes, which 

 commence successively in different portions of the alimentary canal. In 

 the first place, the food is subjected in the mouth to the physical opera- 

 tions of mastication and insalivation. Reduced to a soft pulp, and mixed 

 abundantly with the saliva, it passes, secondly, into the stomach. Here 

 it excites the secretion of the gastric juice, by the influence of which its 

 chemical transformation and solution are commenced. If the meal con- 

 sists wholly or partially of muscular flesh, the first effect of the gastric 

 juice is to dissolve the intervening cellular substance by which the 

 tissue is disintegrated and liquefied. In the small intestine the pancre- 

 atic and intestinal juices convert the starchy ingredients of the food into 

 sugar, and break up the fatty matter into a fine emulsion, by which they 

 are converted into chyle. 



"Although the separate actions of these digestive fluids, however, 



