226 Dynamic Theory. 



2. Fats. Composed of Carbon, Hydrogen and Oxygen only, and containing more 

 hydrogen than sufficient to form water if united with the oxgen which they possess. 

 They include all oils, and vegetable and animal fatty matters. 



3. Amyloids, or starchy substances composed of Carbon, Hydrogen&nd Oxygen only, but 

 with hydrogen and oxygen in just the same proportion as they occur in water. Starch, 

 Dextrin, Sugar, Gum, Glycogena,n animal starch formed in the liver. 



In addition to the Proteids, Fats and Amyloids, which are derived from organized 

 bodies, there are water, salts, earths, and some metals required, which are obtained 

 either from organisms or from the mineral kingdom. 



The composition of Proteid, or albuminoid substances albumen, fibrin, casein, gluten, 

 syntbnin, legumin, &c. is almost exactly the same for all, and they are probably iso- 

 ineric, that is, composed of the same materials put together in molecules of different 

 forms. Their constituents are as follows: Carbon, 53. 5 parts; Hydrogen, 7.1; Nitrogen, 

 15.6; Oxygen, with some sulphur, 23.5, and small amounts of other minerals. 



These food materials are all split up by the different sorts of soluble ferments. 



Among the soluble ferments enlisted in the process of animal diges- 

 tion are pt} T al in, gastric juice, pepsin, pancreatic juice, &c. , which will 

 now be mentioned more in detail. They differ in their offices, having 

 power to affect different kinds of food. As a rule, each has power to 

 cause a split in some class of compounds. 



Ptyalin is a ferment found in the saliva, a secretion which comes 

 into the mouth chiefly from the salivary glands, of which there are four 

 pairs in human anatomy; one pair just in front of the ears called the 

 parotid, one pair in the floor of the mouth under the front part of the 

 tongue called the sublingual, one pair back of the last, in a fold of the 

 mucous membrane, called the lingual, and one pair on either side of 

 these, called the submaxillary. The ducts of these all open into the 

 mouth, and the glands, when stimulated b} r the action of mastication, 

 pour in their secretions to be mingled with the food. The action of the 

 ptyalin is to split starchy and saccharose matters amyloids separat- 

 ing them into glucoses. 



The Gastric Juice is secreted by a number of small branching glands 

 which open upon the surface of the mucous membrane which line the 

 stomach. These are called pep tic glands. The gastric juice is a thin 

 fluid containing lactic or hydrochloric acid and a ferment called pepsin. 

 Pepsin acts only on albuminoids, all of which it splits up and reduces 

 to a pulp the consistency of pea soup, which is then called a peptone. 

 In the process of this digestion the fibrin, and other albuminoids, are 

 first reduced to syntonin, and afterwards, by prolonged digestion, into 

 the peptone. A considerable part of the peptone is fit for assimilation 

 by the tissues of the body without any further digestion, and, therefore, 

 much of it is taken through the membranes of the stomach directly into 

 the blood circulation. The parts of the food that have escaped chemi- 

 cal reduction by the ptyalin of the saliva or the pepsin of the gastric 

 juice, will nevertheless be found to be dissolved by the gastric acids and 

 by the mechanical movements of the stomach. The name given the 

 food in this condition is chyme. After a time this chyme passes through 

 the lower gate of the stomach, called the pylorus, into the upper part 



