The Animal substances which have been the objects of the chemist are, the blood, the gastric and pancreatic juices, the milk, the sebacic acid, the bile, the urine; the prussic, zoonic, formic, and bombic acids; the hard parts of animals; the humours of the eye; cartilages; brain; synovia; tears; mucus of the nose, &c; cerumen of the ears; saliva; pus; semen; sweat; liquor amnii; eggs; hairs; feathers, and silk. These are more particularly the object of this work, and have been or will be considered in separate articles. We need scarcely repeat, that nitrogen, or azote, is the distinguishing principle of animal substances; and have already observed that their component parts are nitrogen, hydrogen, carbon, and oxygen.
The ultimate analysis of animal substances is peculiarly embarrassing, on account of the extensive combination of their elements, for the simplest agent produces numerous transformations; many of which, from the rapidity of their progress, escape us, and the last results are only obvious. The agent employed, most successfully, by Scheele, Bergman, and Berthollet, is the nitric acid; and the result, as we have often mentioned, is the evolution of azote in large quantities. The consequences are also a change in the acid; the copious production of ammonia; carbonic, oxalic, and malic acids; the transformation of one portion of these matters into fat; and of another into a yellow, bitter substance, the bitter of Welther.
The effects, however, vary according to the strength of the acid, the duration of its action, and the kind of substances examined by its means. These varieties have been lately the subject of MM. Fourcroy and Vauquelin's inquiries, and we shall take this opportunity of stating their results. The particular experiments have not yet been published.
The nitrous acid, from its first action, changed the muscular flesh into a yellow substance, with little taste, though still sensibly acid, and very imperfectly soluble. When the action was longer continued, the result was a matter equally yellow and acid, but very bitter, and very soluble. By a still longer continued action, the matter was soluble, inflammable, and fulminating, not only by heat but by percussion.
Indigo furnished a similar substance, and still more copiously than muscular flesh. Haussman and Welther long ago discovered it; and MM. Fourcroy and Vau-quelin attribute it to the separation of the azote, and to the combination of the hydrogen and carbon of the flesh, with the excess of oxygen furnished by the acid. They suspect that the yellow substance which tinges the bile, is equally produced by the separation of the azote and the union of the other ingredients, furnished probably by the blood. Yet this appears less probable; since the blood which is to furnish the bile is carried by a very circuitous course, after it has received the oxygen from the air, and the contents of the vena portae abound seemingly more in azote than in oxygen.
While we are speaking of animal substances, it may not be uninteresting to add the experiments of those chemists on the smut of wheat. They found, in this degenerated corn, a green oil of the consistence of butter; phosphoric acid, in part combined with magnesia; some lime and ammonia; carbon, and a vegeto-animal substance, exactly like that which is produced in the decomposition of the gluten of wheat by putrefaction.
They consequently conclude, that the smut is the residuum of the farina, decomposed by a putrid fermentation; and suspect that it arises from an over proportion of animal manure, assisted by a hot and moist season at the period of its flowering, or the formation of the grain.
What may be further requisite for the different facts relating to medical chemistry, may be found under Affinity, q. v.