not be easy to decide which ingredient predominates, or gives its peculiar qualities to the compound. We shall also find that if we examine a series of secreted fluids, we shall perceive that they all closely resemble each other in what may be termed their specific properties, yet that those at each extremity of the series may so far differ from that which was adopted as the standard or type of the rest, that the resemblance may be more nominal than real, and the difference may at length proceed so far, that they may even bear a nearer resemblance to some other class than to that in which they are placed. Another circumstance, which causes considerable embarrassment in a chemical arrangement of the secretions, is, that the same gland, in different states of the system, produces substances of a very different nature, and when the affection amounts to the degree which constitutes disease, entirely new substances are frequently formed, unlike any thing which previously existed, and which, although they must be regarded as altogether morbid effects, yet they are strictly entitled to the appellation of secretions, and which indeed, had we a complete knowledge of the subject, would form the most interesting object of our investigation, by making us acquainted with the nature of the morbid action which had taken place, and even the amount of the deviation from the standard of health. This, however, in the present state of our knowledge, we are quite unable to accomplish. In order to take a complete view of the subject, it would be necessary to examine the secretions in all their

various states, to mark the gradations from the healthy to the morbid condition, and to observe what new characters were assumed in each of them.

Taking into account all these circumstances, and bearing in mind that the present state of our knowledge is confessedly imperfect, it will be sufficiently evident, that any arrangement which I can propose must be necessarily incomplete; but I am not, on that account, deterred from making the attempt, because, if the method itself be fundamentally correct, even an imperfect view of it will be useful, by teaching us what parts require further elucidations, and instructing us in the best method of accomplishing it. The classes into which I propose to arrange the secretions, are the eight following; the aqueous, the albuminous, the mucous, the gelatinous, the fibrinous, the oleaginous, the resinous, and the saline."

9 I shall insert in this place the arrangements of the secretions that have been proposed by some of the most eminent of the modern physiologists. Sabatier and Boyer, with most of the French anatomists, adopt the division of the secretions into recrementitious and excrementitious, to which they generally add an intermediate class. Boyer places the following among the recrementitious humours, as he styles them; blood, lymph, jelly, fibrous matter, fat, marrow, matter of internal perspiration (serous transudation), and the bony juice; among the excrementitious, the matter of insensible perspiration, sweat, discharge from the nose, ears, and eyes; and in the third or intermediate class, tears, saliva, milk, bile, pancreatic juice, and semen; Anat. t. i. p. 8, 9. Magendie divides them into exhalations, follicular secretions, and glandular secretions, but he candidly acknowledges the imperfection of his method; each of the classes is subdivided into numerous species; Physiol. t. ii.

§ 2. Account of the Secretions.

The first class of secretions, the aqueous, are those that consist almost entirely of water, where the properties of the substance depend upon its watery part, or when any other ingredient which it may contain is in

p. 343. et seq. Plenk divides the humours of the body into crude, sanguine, lymphatic, secreted, and excrementitious; the 'secreted fluids he arranges under the heads of milky, watery, mucous, albuminous, oily, and bilious; Hydrol. p. 31, 2. Richerand arranges them into the six classes of saline, oily, sapona. ceous, mucous, albuminous, and fibrinous; Physiol. § 88. p. 235. Blumenbach makes the following classification; milk, the aqueous fluids, the salivary, the mucous, the adipose, and the serous, while the semen and the bile are supposed to be substances sui generis; Inst. Phys. § 467. Berzelius adopts the old division into secretions and excretions, a division which is founded rather upon the final cause of their formation, than upon their properties, or the mode of their production; he remarks, however, that the secretions are all alkaline, while the excretions are acid, a remark which, I conceive, will scarcely be found to apply in all cases; Med. Chir. Tr. v. 3. p. 234. Dumas classes the secretions in four divisions, according to the more or less simple structure of the organs which produce them; those that are formed without any specific organ, by the most simple organ, by a gland, and by the complete secretory apparatus; Physiol. t. ii. p. 15..8. Dr. Young arranges the secreted fluids into the classes of aqueous, urinary, milky, albuminous, mucous, unctuous, and sebaceous; Med, Lit, p. 109.

The writer of the article "Anatomy" in Brewster's Encyclopedia, has drawn up the following arrangement of the secreting and excreting organs, with the fluids which they produce, which is valuable as pointing out the relation which exists between them. They are first divided into secreting surfaces and secreting organs. Of the surfaces we have three divisions;

too small a quantity to give it any specific characters. The only two secretions which fall under this class, are the cutaneous perspiration and the aqueous exha→ lation from the lungs. Of the cutaneous perspiration I have already given some account in the two last chapters, where I have stated, that under ordinary circumstances, a portion of water is exhaled from the

1. Those which separate matters already formed in the blood, viz. the serous, producing serum or coagulable lymph, and the cellular, producing serum and fat; 2. Those which separate from the blood matters that are little changed, viz. synovial membranes, forming synovia and mucous membranes, forming mucus; 3. Excreting surface, viz. the skin, giving out the matter of perspiration. The secreting glands are arranged under the four heads of such as are attached to the organs of sensation, those of digestion, those of reproduction, and glands that are partly secretory and partly excretory. Under the first head we have the papilla of the tongue, which secrete a watery fluid, the ceruminous glands which secrete the ear wax, and the lachrymal which secrete the tears. Under the second head we have the parotid, submaxillary, and sublingual glands, which secrete saliva, the pancreas, which secretes its peculiar juice, the spleen, to which no secretion is assigned, and the liver, which produces the bile. Under the third head we have the testes, prostate gland, and the mammæ, which respectively secrete the seminal fluid, the prostatic fluid, and the milk; and under the fourth head, we have the kidneys, which produce the urine, and the renal glands, which produce a blackish fluid; yol. i. p. 830, 1. In addition to the eight classes of secretions which are enumerated above, I am disposed to think that we might with propriety admit a ninth class of aeriform fluids, of which the air in the swimming bladder of fishes may be adduced as an example; upon strictly technical principles, the air of expiration may be placed in the same division, See remarks by Dr. Baillie; Works by Wardrop, v. i. p. 69. et seq.

surface of the body in the form of an invisible vapour; but when its quantity is by any means increased, it assumes the state of a fluid, and is collected in drops on the skin. It does not appear that its chemical nature is different in these two states, although it is not very easy to decide absolutely on this point, in consequence of the difficulty of obtaining any quantity of it when in the state of vapour. The sensible perspiration may be procured in sufficiently large quantity, and has been examined by several eminent chemists, but except the water, it seems doubtful whether any of the ingredients that have been detected in it are essential to its nature. It appears probable that the perspiration differs considerably according to the states of the system, not only as affected by various morbid actions, but from internal causes, or the effect of internal agents upon it, and there is likewise reason to believe, that it may be habitually different in different individuals. Upon all these points, however, it must be confessed that we have no very accurate information, as the attention of those who have examined this substance has been almost exclusively confined to ascertain its quantity, and the pathological effects which have been supposed to be the result of its discharge from the system. There is, however, reason to suppose, that these have been very much exaggerated, and that many discases which were conceived to depend upon the suppression of the cutaneous perspiration, are owing to an entirely different cause, of which the