26 SUBDIVISIONS OF PHYSIOLOGY. 



itself with, those great truths which concern the human family most 

 closely, and is bringing into the region of physical demonstration the ex- 

 istence and immortality of the soul of man, and furnishing conspicuous 

 illustrations of the attributes of God. 



CHAPTEE II. 



OF FOOD. 



The natural Subdivisions of Physiology. Of Food: its Sources and Classification its Value not 

 altogether dependent on its Composition. Of Milk: its Composition, and Use of its Water, 

 Casein, Sugar, Butter, and Salts. Variations in the Composition of Milk. Of Bread. Of 

 mixed Diets. Of the embryonic Food of Birds. Nutrition of carnivorous and herbivorous 

 Animals. Food formed by Plants and destroyed by Animals. Uses of mixed Food and Cook- 

 ing. Absolute Amount of Food. 



PHYSIOLOGY possesses a very great advantage over many other sciences 

 Subdivisions of in offering its leading problems and doctrines in a certain 

 physiology. well-marked order or sequence, a connected whole, with only 

 here and there points of digression, but those points often of very striking 

 interest. Thus pursuing the train of reflections entered on in the pre- 

 ceding chapter, we should have to consider the nature of the food, the 

 manner, of its preparation by the process of digestion, the mechanism by 

 which it is taken up from the cavities in which it has been so prepared, 

 and that by which it is distributed to every part. We should have to 

 show the way in which it becomes incorporated as a portion of the living 

 mass, its duration in that condition, and the manner of its decay. We 

 should have to show by what physical means and through what mecha- 

 nism the air is introduced to effect the destruction of the dying parts, and 

 how, as the consequence of this, a fixed temperature is maintained. The 

 causes which lead to variations of this temperature, and the manner in 

 which the wasted products are removed by the skin, the lungs, the kid- 

 neys, might next obtain our attention. The complicated machinery nec- 

 essary to accomplish all these purposes requires to be made to act in uni- 

 son in all its different parts, a condition which introduces to us the nerv- 

 ous system. A consideration of the structure and gradual development 

 of this system leads to the structure of the various organs of sense, and 

 to the operations of the intellectual principle itself. Thus in succession 

 we should have to treat of digestion, absorption, circulation, respiration, 

 secretion, nutrition, and innervation, and to close the whole with the con- 

 sideration of reproduction. This is the order which I propose to follow, 

 and shall devote this chapter to the nature and qualities of the food. 



