38 PROXIMATE PRINCIPLES IN GENERAL. 



ferent character from the chemical constitution of an oxide or a salt. 

 Whenever, therefore, we meet with the analysis of an animal fluid, in 

 which the relative quantity of its different ingredients is expressed in 

 numbers, we must understand that such an analysis is always approxi- 

 mative, and not absolute. 



The proximate principles are naturally divided into five different 



The first of these classes comprises all the proximate principles which 

 are purely INORGANIC in their nature. These principles are derived 

 mostly from the exterior. They are found everywhere, in the inorganic 

 world as well as in organized bodies ; and they present themselves under 

 the same forms and with the same properties in the interior of the 

 animal frame as elsewhere. They are crystallizable, and they present 

 very definite chemical characters and have a comparatively simple chemi- 

 cal constitution. They are compounds, in simple proportions, of the 

 ultimate chemical elements, hydrogen and oxygen, the metals of the 

 alkaline and earthy salts, sulphur, phosphorus, chlorine, and, in general 

 terms, of the ingredients of mineral substances. They comprise water, 

 which is the most abundant of its class in the animal frame, sodium 

 and potassium chlorides, phosphates, and sulphates, alkaline carbonates, 

 the salts of lime and magnesia, together with combinations of a few 

 other of the metallic elements in minute quantity. 



The second class of proximate principles consists of the HYDROCAR- 

 BONACEOUS SUBSTANCES of organic origin. They are distinguished from 

 inorganic matters first by the fact of their containing carbon in large 

 proportion as one of their immediate constituents, associated always 

 with hydrogen and oxygen, but with no other chemical element. They 

 are always either crystallizable, or else readily convertible into other 

 crystallizable members of the same group. Their chemical composition 

 is less simple than that of inorganic substances, but it is still sufficiently 

 definite, and their chemical characters are well marked and easily recog- 

 nizable. They first make their appearance in the interior of organized 

 bodies, and are not found in the inorganic world, excepting as the 

 remains or products of animal or vegetable life. To this group belong 

 the several varieties of starch, sugar, and oil. 



The third class comprises the ALBUMINOUS, or nitrogenized proximate 

 principles. These substances derive their name from the albumen or 

 white of egg, which was one of the earliest to be studied, and which 

 was long considered as a kind of representative of the whole class. 

 They differ from the substances of the two preceding groups, especially 

 in the fact that they contain nitrogen as an ingredient, in addition to 

 the three elements of the hydrocarbonaceous matters. They are exclu- 

 sively of organic origin, appearing only as ingredients of the living bod} T . 

 Their chemical constitution, furthermore, is a complicated one that is, 

 their four elements are united with each other in such a way as to form 

 compounds of a very high atomic weight. Their chemical characters 



