98 VARIOUS MODES OF EXISTENCE OF CHEMICAL COMPOUNDS 



of Fishes ; whilst that of the Ox is equally well distinguished 

 from that of the Sheep, and the flesh of the Turkey from that 

 of the Partridge. It is the same with the subjects of the 

 Vegetable Kingdom ; many different classes and genera, and, 

 still more, different species of plants produce Wood, Gum, 

 Starch, and Sugar ; but the timber of the Oak is distinct in its 

 nature and properties from that of the Fir, as is the gum of the 

 Acacia from that of the Cherry-tree, the starch of Wheat from 

 that of the Potatoe, and which brings us to our present sub- 

 ject, the Sugar of the Sugar-cane from that of the Maple- Tree 

 or the Beet-root." * 



* The above statement, it may be well to remark, lest rny views upon the 

 subject should be misunderstood by proficients in chemistry and physiology, 

 was made with reference to the substances which are known to us as results 

 of organization only, and it was even confined to them, as they occur in 

 nature, forming distinct organs, or parts of organic structures, or proximate 

 chemical elements of them, in the form and peculiar condition in which they 

 actually exist in organized beings. From the connection in which it was made 

 in the Lectures, it would be understood in a general sense agreeing with this, 

 by the young pupils to whom it was addressed. It is not applicable, at least 

 in the form given in the text, to those earthy and alkaline salts which occur 

 in the Mineral as well as in the Animal and Vegetable Kingdoms, and which 

 can also be produced in the laboratory of the chemist, in a state as perfect 

 as that in which they occur in nature. Nor is it applicable to all the com- 

 pounds which result from the analysis of Animal and Vegetable fluids or tex- 

 tures, and which, in the present state of organic chemistry, must be regarded, 

 provisionally, as the proximate chemical elements of those fluids or textures ; 

 but it is applicable, I apprehend, to all the proximate organic elements as 

 they exist in the living structures (and to a certain extent after the death also) 

 of the beings which they contribute to compose. Thus, although the sugar of 

 milk, Cholesterine, and Urea, (and animal fat also, if the experiments of 

 Be*rard and Dobereiner on its artificial production be conclusive,) may be 

 regarded as definite and stable compounds, since they are all crystallizable, 

 yet as they exist in the living body secreting them, they will be different, I 

 conceive, in every species of animal in which they are found ; while to 

 Fibrine, Albumen, Gelatine, and many other animal substances, the same 

 reasoning is still more applicable. And though the pure woody fibre be 

 known to consist of equal parts of water (or its elements) and carbon, in 

 every kind of wood, yet, in the form or condition in which that principle 

 enters into the composition of the wood of the various trees, it must be 

 different in each species. 



It would appear from an extensive review of the subject, that the definite 

 compounds in which no metallic substance is essentially present (for there 

 is no other character by which they can be universally designated) which 

 exist in, or result from the analysis of, the subjects of nature, increase 

 in stability and in number as we descend in the scale of organization, if 

 we compare together the three kingdoms of nature, in this respect. Thus 

 no principle of animal life, devoid of metallic elements, is of so stable a 

 constitution or perhaps of so definite a nature, as the woody fibre and the 

 sugar of vegetables ; or, to state the truth in the most cautious terms, 

 it is far more easy to obtain such principles from vegetables than from 

 animals ; while the mineral kingdom is entirely constituted of definite and 

 stable compounds. The paucity of such compounds in the animal king- 



