136 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



constant ingredients of animal substances, but they are present in such 

 small amounts, or in such variable quantities, that their importance has 

 not been clearly established. These are magnesium chloride, calcium 

 fluoride, ammonium carbonate, magnesium-ammonium phosphate, calcium 

 sulphate, silicon, iron, manganese, and copper. 



In vegetable tissues nearly all the constituents of the animal cell are 

 found deposited or in solution. They serve to give greater solidity to 

 the so-called skeleton of plants, and are also without doubt of importance 

 in the vital processes of vegetable protoplasm. Thus, it has been found 

 that the amount of albumen in germinating seeds stands in direct propor- 

 tion to the amount of phosphate which the plant receives as food ; also, 

 that without potassium salts plants cannot grow. Their interest to us as 

 constituents of vegetable organisms is simply dependent upon their ren- 

 dering such substances suitable for animal foods. They will therefore 

 receive the necessary consideration under the subject of Foods. 



II. THE CHEMICAL PROCESSES IN CELLS.* 



The great mass of organized bodies, both animal and vegetable, are 

 what might be described as carbonic acid compounds, associated in vari- 

 able amounts with hydrogen, oxygen, and nitrogen. Plants are able, 

 from inorganic substances, such as CO 2 , H 2 0, N0 3 H, NH,, H 2 SO 4 , P 2 O 6 , 

 to develop organic compounds, the difference between such bodies as 

 entering into and as leaving plants depending merely upon the difference 

 in their proportion of oxygen. The inorganic bodies, which serve as 

 food for plants, are what are known as combustion products ; that is, 

 they already contain the maximum quantity of oxygen which is able to 

 enter into their composition. Organic bodies, on the other hand, contain 

 in all cases less oxygen than will satisfy the affinities of their constituent 

 elements. They therefore are capable of undergoing further oxidation, 

 or, in other words, may be said to be combustible. The plant-cell, there- 

 fore, must be able to deoxidize the inorganic compounds of its food and 

 set free oxygen ; and this deoxidizing force must evidently be greater 

 than the affinity exerted by the oxygen for the elements with which it 

 was in composition. This deoxidizing power possessed by plants is only 

 capable of manifestation in the sunlight, and is a function of the green 

 coloring matter, the chlorophyll of plants. The animal cell, on the other 

 hand, in its nutritive operations exhibits the reverse process of oxida- 

 tion. The inorganic compounds which in the vegetable cell become 

 organic, that is, deoxidized, in the animal cell become again oxidized and 



* For the preparation of this section special acknowledgment is due to Wurtz, 

 " Chimie Biologique ; " Wundt, " Lehrbuch der Physiologic ; " Gorup-Besanez, " Physi- 

 ologische Chemie ; " Ranke, " Grundziige der Physiologic ; " Hoppe-Seyler, " Physiolo- 

 gische Chemie ; " Schiitzenberger, " Fermentation ; " Nageli, " Theorie der Garung." 



