whether the jelly be itself organized, a supposition which is rendered probable by the large proportion which it forms of certain substances. In isinglass, for example, the insoluble part is not more than about 1.5 per cent. of the whole, and unless we conceive the jelly, in this case, to form a mere concretion (an idea which is inconsistent with all our conceptions of the constitution of the animal body), we are almost reduced to the necessity of supposing the jelly itself to be organized. Like the albumen, jelly is nearly free from salts or any other extraneous substances.

The fifth class of secretions, the fibrinous, are so named from their resemblance to the fibrin of the blood, and from this being the probable source whence they are immediately derived. They differ from those that have been hitherto examined in the circumstance of their containing a larger proportion of nitrogen, or being, as it is said, more completely animalized, in their chemical composition, while in their physical structure, they retain the peculiar fibrous texture of the substance from which they are produced. In this class we must place the muscular fibre under all its various forms, which, whether con

5 MM. Guy-Lussac and Thenard's analysis of fibrin is as follows:

Carbon 53.360, Oxygen 19.685, Hydrogen 7·021, Nitrogen ́19934; thus giving us 2.946 per cent. more nitrogen than in jelly, and 4.229 per cent. than albumen; Researches, t. ii. p. 350; Thenard, Traité, t. iii. p. 523, and t. iv. p. 305; Children's Thenard, p. 357. It is generally admitted that the ele mentary constitution of the pure muscular fibre is identical with that of the fibrin of the blood.

stituting the long fibres of the proper muscles, or the short ones of the muscular coats, appears to possess exactly the same chemical composition, and nearly the same physical form and arrangement with the fibrin of the blood." This is one of those cases where the effect of secretion appears to consist merely in separation, and this we may conceive to be accomplished by the separated substance having been simply discharged by the mouths of the capillary arteries, and deposited in its appropriate situation in the body, so as to be adapted, without any farther change, to the office which it is afterwards to serve in the animal œconomy.

It may be questioned whether there be any substance except the muscular fibre which ought to be arranged under this division. The other constituents of the body which exhibit a fibrous structure are, for the most part, what have been already included among the albuminous secretions, as being formed of this substance in the coagulated state, so that, upon the principles of the chemical arrangement, it appears necessary to include them in this division. It must, at the same time, be admitted, that the difference between the elementary constitution of albumen, jelly, and fibrin, is not very considerable, nor is it

6 Cuvier indeed observes, Leçons, t. i. p. 90, 1. that fibrin is not found in any of the food that is taken into the stomach, and concludes that it is formed by respiration; the operation of this function he supposes is to remove carbon and hydrogen from the blood, and consequently to leave in it a larger proportion of nitrogen.

very decisively established, yet there appears reason to conclude that an essential difference between them does exist. There are some other parts of the body which also possess a fibrous texture, such as the basis of the cutis, but this would seem to have more relation in its chemical composition to albumen or to jelly, than to fibrin. The fibrous coat of the arteries belongs to the class of substances which we are now examining, as also the fibres of the iris," and probably both of these must be considered as nothing more than mere varieties of the muscular structure. Four croy and Vauquelin have described a peculiar substance of a fibrous texture, which is found in the seminal fluid, and would appear to compose the speeific part of this secretion, which, perhaps, ought to be referred to this class. A fibrous substance was

I have remarked above, v. i. p. 399, that Prof. Berzelius and Dr. Young conceive the chemical composition of these parts to differ from that of the proper muscular fibre; with every feeling of respect with such high authority, it appears to me that the experiments are not sufficiently decisive to enable us to form an opinion upon the subject. It would be desirable to compare the elementary analysis of the muscles of fishes and of the mollusca with those of the mammalia, in order to ascertain with what variety of chemical composition muscular contrac tility can be connected; we should probably find some difficulty in reconciling the chemical with the physiological arrangement.

8 Ann. Chim. t. ix. p. 64. et seq.; Thomson's Chem. t. iv. p. 534. .7; Thenard, Traité, t. iii. p. 694, 5. The nature and functions of the spermatic animalcules, which formerly gave rise to so much controversy, Blumenbach, Inst. Phys. § 528. and note (G), and the existence of which appears to be confirmed by the late observations of MM. Prevost and Dumas, Edin.

found by Dr. Marcet composing the basis of a urinary calculus, and similar substances have been occasion, ally met with in other morbid concretions, which are lodged in the different cavities or passages of the body; but it is probable that these were merely por tions of fibrin that had been effused from a ruptured vessel, and not the result of any new action of the vessels.

We now arrive at a class of bodies that are more distinct from any of those that are found naturally existing in the blood, and which we may therefore suppose to be the result of a more elaborate or com plicated action of the secretory organs, the oleaginous secretions, those that derive their essential character from the presence of an oily ingredient. These compose a numerous, and at the same time, a considerably varied class of substances, in some of which the oil

Phil. Journ. v. vii. p. 247, will be more properly considered hereafter,

9 Perhaps the synovia ought to be included among the fibrinous secretions, as we are informed by Margueron, that its specific character depends upon a substance of a fibrous texture, but the experiments do not enable us to decide, whether it be of the nature of muscular fibre or of membrane; Ann. Chim. t, xiv. p. 123; Thomson's Chem. y. iv. p, 532..4; Thenard, Traité, t.iii. p. 685,6; Henry's Elem. v. ii. p. 433, 4; See Vauquelin's Analysis of Synovia from an elephant; Ann. Chim. et Phys. t. vi. p. 399. et seq.; and Journ. Pharm. t. iii. P. 289. et seq.

I had once an opportunity of examining a fluid from the cavity of the knee joint; it consisted of water holding in solution about 5 per cent of albumen, in which a number of flakes or masses were floating, that appeared to be composed of coagulated albumen; Med. Chir. Tr. v. iv. p. 74.

is nearly in a state of purity, or at least forms the greatest part of the body in question, while in the others, the oil is mixed with other animal principles, in such a manner, that it is not easy to decide in which division the substance under consideration ought to be placed. As a matter of convenience I have thought it better to place every substance in this class, that contains oil in any notable proportion, or of which any of the specific characters depend upon oil, although the actual quantity of it may be less than that of some of the other ingredients. Of the oleaginous secretions, the first that claims our attention, both from its quantity and the state in which it exists, is the fat of all kinds, which is found connected with the muscles and many of the viscera. In its chemical constitution fat appears to agree very nearly with the expressed vegetable oils; like those it varies in its consistence, or rather in its freezing point, so as, in the ordinary temperature of the atmo sphere, to be found sometimes in a solid state, as is the case with suet and tallow, and at other times perfectly fluid, as we find it more particularly dif fused through the cellular texture of the cetacea. We are not acquainted with any apparatus that is appropriated to the secretion of oil, nor are there any facts which can enable us to decide positively upon the mode of its formation. As a substance of an oily nature has been said to enter into the composition of the chyle, and as the formation and deposition of fat appear to bear a relation to the quantity of chyle that is produced, it has been conjectured that