matter which will serve for the formation of carbonie acid in the lungs, when from any cause there is a deficiency of the usual supply as derived from the chyle. In ordinary cases, the thoracic duct pours into the venous trunks a quantity of chyle sufficient both for the growth and the nutrition of the body, and for the consumption of carbon by the lungs, but if, from any cause, the supply is insufficient, the absorbent system takes up the adipose matter from its various receptacles, and introduces it into the sanguiferous system, where it serves for the generation of carbonic acid, and consequent production of

animal heat.*

Besides the fat under its ordinary forms, and in its various states of solidity, the marrow belongs to this class of secretions," and also the substances which are

4 See the elegant inaugural dissertation of Dr. Skey, “De Materia Combustibili Sanguinis;" also Prof. De la Rive, "De Calore Animali," passim. That the fat is the origin of the inflammable matter which serves to maintain the animal heat, was maintained by Moschati, but his opinion was obscured by much false reasoning and incorrect experiment; see Journ. Phys. t. xi. P. 389.

s Marrow has lately been analyzed by Berzelius, and was found to consist of the following substances:

produced from the sebaceous glands that are found in various parts of the body. These probably exist in a greater or less quantity in all animals, and impart to them their specific odours, many of which are very peculiar and powerful, and are connected with some of the most important instincts of the brute creation. Among the oleaginous secretions we ought probably to place the cholesterine which forms the basis of biliary calculi, although it differs from fat in some of its chemical relations, and it may moreover be doubted whether it be not formed after the substance of which it is composed leaves the vessels, and is simply lodged in the biliary ducts."

We have several other secretions which owe some of their peculiar characters to the oil which they contain. Among these is milk, a very compound fluid, which is formed principally of oil in combination with albumen, so united as to form a kind of emulsion. By mere rest the greatest part of the oil separates, the albumen still remaining combined with the water and the other ingredients, from which it cannot be detached without the intervention of a chemical re-agent, which, by coagulating it, renders it easily separable by mechanical means. Milk likewise contains a saccharine matter, which assists in adapting it for its appropriate office, that of nourishing the young animal immediately after birth, and

6 See Chevreul, Ann. de Chim. t. xcv. p. 7.. 10. and Ann. de Chim. et Phys. t. vi. p. 401. Spermaceti and wax are also adipose secretions, but they are not produced by the organs of the human subject.

may also have the farther use of contributing to preserve the milk in a fluid state, by rendering the emulsion of albumen and oil more perfect. Milk is secreted from a body which possesses all the appropriate parts of the glandular structure on a large scale, and appears to be possessed of a very elaborate organization. Were we to reason from the analogy. of the other secretions, we might be led to form a conclusion, which is probably very different from the common opinion, that of the three substances which essentially compose milk, the sugar is the one for which the glandular apparatus is more particularly required. The albumen does not appear to differ essentially from the albuminous part of the serum, and we do not find that oil, in other parts of the system, requires any distinct gland for its formation.

It may, indeed, be thought an objection to this idea, that the kidney, in a certain morbid state, acquires the property of secreting sugar, from which it would seem that this substance, although so different in its nature from any of the constituents of the blood, may yet be formed from it, without any thing very peculiar or specific in the structure of the secreting organ, so that we might be inclined to ascribe the effect, rather to some alteration in the fluid that is brought to the part, than to the action of the organ itself. It is to be observed, however, that the sugar of diabetes exactly resembles vegetable sugar, while the sugar of milk differs from it in the proportion of its elements, and likewise in the result of the action of nitric acid upon it, which

produces mucic acid with the sugar of milk,' and oxalic acid with the sugar of diabetes."

7 The ultimate analysis of vegetable sugar, as given by the latest experiments, is as follows;

It would appear from these analyses, that the sugar of milk contains more hydrogen and oxygen, and less carbon, than vegetable sugar. Dr. Prout, however, gives a somewhat different account of their comparative composition; he says, "sugar of milk yielded very near the same results" with vegetable sugar, and that their apparent difference is "to be attributed to the influence of the presence of minute portions of foreign matters, analogous, for example, to what occurs in the inorganic kingdom, in the mineral called arragonite;" Med. Chir. Tr. v. viii. p. 538. With respect to diabetic sugar, Dr. Prout could not find it to differ, in its ultimate analysis, from vegetable sugar; p. 537. Dr. Ure, on the contrary, finds its elements to be considerably different; he gives the following proportions;

As to the question of identity in this case, perhaps we ought

Research. t. ii. p. 289.

↑ Ann. Phil. v. v. p. 264. .6.

Med. Chir. Tr. v. viii. p.536,7. § Phil. Trans. for 1822, p. 467. Research. t. ii. p. 293.. ** Ann. Phil. v. v. p. 266.

++ Phil. Trans. for 1822, p. 467.

The milks of different kinds of animals have been minutely examined by various chemists, and although they have been found to differ considerably in the amount of their solid contents, and in the proportion which their constituents bear to each other, they essentially agree in their composition, as consisting of albumen, oil, and sugar, dissolved or suspended in a large quantity of water. In many cases we can perceive a relation between the nature of the milk and of the animal which is to be nourished by it, and we may remark generally that this fluid appears to be the combination, of all others, the best adapted for supplying the elements of nutrition in the early stages of existence, when there is a necessity for a copious supply of nutriment, while the digestive organs are in a state of extreme delicacy. Berzelius, who has lately analyzed cow's milk, has found it to contain 8 per cent. of the earthy phosphates, an evident provision for the formation of bone, while it would appear to differ from most of the other secretions, which consist principally of albumen, in containing no soda, either in the combined or uncombined state. The temporary existence of this secretion at a period when its utility is so obvious, with its cessa

to depend more upon the effects produced by nitric acid, than upon the results of the elementary analysis. We are informed by Vogel, Ann. Chim. t. lxxxii. p. 156, that sugar of milk may be converted into a sugar resembling that from vegetables, by being digested with very dilute sulphuric or muriatic acid, thus furnishing an additional analogy between animal sugar and gum; See Thenard, Chin. t. iii. p. 549..1.

8 The following is Berzelius's analysis of skimmed cow's milk: