24 NATURE AND OBJECTS OF PHYSIOLOGICAL SCIENCE. 



which last, indeed, it is always found combined, in the Albumen, Fibrine, 

 &c., that are commonly regarded as the organic constituents of the 

 Animal tissues. The second of the chief proximate principles, termed 

 G-elatine, is largely diffused through the Animal body ; but the tissues 

 which are composed of it possess a simple fibrous structure, and a purely 

 mechanical function ; and no vital action seems to take place in them, 

 subsequently to their first production. It consists of 13 Carbon, 10 

 Hydrogen, 2 Nitrogen, and 5 Oxygen ; and it is principally characte- 

 rized by its solubility in hot water, and by the insolubility of its com- 

 pound with tannic acid. 



14. We shall hereafter dwell more in detail upon the Chemical Con- 

 stitution of the Animal tissues and products (CHAP, in.) These sub- 

 stances are only noticed here, in illustration of the general statement, 

 that the "proximate principles" of Animal and Vegetable bodies (that 

 is, the simplest forms to which their component structures can be 

 reduced, without altogether separating them into their ultimate ele- 

 ments), are of extremely peculiar constitution ; being made up of three 

 or four elements, of -which the atoms do not seem to be united two by 

 two, or by the method of binary composition, but of which a large 

 number are brought together to form one compound atom, of ternary 

 or quaternary composition. This compound atom, like Cyanogen, and 

 many others derived from Organic products, acts like a simple or ele- 

 mentary one in its combinations with other substances. It is worthy 

 of remark, however, that, in this respect as in others, the Vegetable 

 kingdom is intermediate between- the Animal and the Mineral. For 

 whilst Proteine and Gelatine are remarkable, not only for containing 

 four elements, but for the very large number of atoms of these compo- 

 nents which enter into the single compound atom of each ; the Cellu- 

 lose of Plants is much simpler in its composition, since it includes only 

 three elements, and the numbers which represent their proportions are 

 smaller. And further, the proportions of the components of Cellulose 

 are themselves such as suggest the idea of simplicity in their method of 

 combination, the union of water and carbon in the common binary 

 method ; an idea which is confirmed by the mode of its original pro- 

 duction, which indicates a direct union of carbon with water ; as well as 

 by the fact, that the chemical difference between Cellulose and nume- 

 rous other substances found in Plants, may be represented by the simple 

 addition or subtraction of a certain number of atoms of water, and that 

 the chemist can effect an actual conversion of the former into certain of 

 the latter, by means which are calculated to effect such an addition or 

 subtraction. 



15. We shall hereafter see that Vegetables are intermediate between 

 the Animal kingdom and the Inorganic world in another most important 

 particular the nature of the chemical operations they effect ; for it is 

 their function to combine the oxygen, hydrogen, carbon, and nitrogen, 

 of the Inorganic world into Organic Compounds ; which not only serve as 

 the materials of their own growth, but also as the food of Animals, whose 

 existence is entirely dependent upon them, since they possess no such 

 combining power. It is from the Water, Carbonic Acid, and Ammonia, 

 supplied by the atmosphere and by the soil in which they are fixed, that 



