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soon as an action of aspiration was exerted upon it by the cuppingglass.
2. Into the crural veins of two dogs;—one of which breathed naturally, and the other was circumstanced as in the last experiment, they injected the essential oil of turpentine. In the first of these, the substance was soon apparent in the pulmonary transpiration; and, on opening the body, it was discovered, that the turpentine had impregnated the lung and the pleura much more strongly than the other tissues. In the other animal, on the contrary, the odour of the turpentine was scarcely apparent in the vapour of the lungs; and, on dissection, it was not found in greater quantity in the lungs, than in the other tissues;—in the pleura than in the peritoneum.
From the results of these experiments, MM. Breschet and Edwards conclude, that each inspiratory movement constitutes a kind of suction, which attracts the blood to the lungs; and which causes the ejection, through the pulmonary surface, of the liquid and gaseous substances that are mingled with that fluid, more than through the other exhalant surfaces of the body.
In their experiments, these gentlemen did not find that the exhalation was effected with equal readiness in every part of the surface, when the cupping-glass was applied in the manner that has been mentioned. The skin of the thigh, for example, did not indicate the odour of camphorated alcohol, as that of the region of the stomach.
The chymical composition of the pulmonary transpiration is probably nearly identical with that of the sweat; appearing to consist of water, holding in solution, perhaps, some saline and albuminous matter; but our information, on this matter, derived from the chymist, is not precise. Chaussier found, that by keeping a portion of it in a close vessel, exposed to an elevated temperature, a very evident putrid odour was exhaled on opening the vessel. This could only have arisen from the existence of animal matter in it.
The pulmonary transpiration being liable to all the modifications that apply to the cutaneous, it is not surprising that we should meet with so much discordance in the estimates of different individuals, regarding its quantity in a given time. Hales valued it at 20 ounces in the twenty-four hours; Menzies at 6 ounces; Abernethy at 9 ounces; Lavoisier and Seguin at 171⁄2 ounces, poids de marc; Thomson at 19 ounces, and Dalton at 1 pound 8 ounces.
The uses it serves, in the animal economy, are identical with those of the cutaneous depuration.
9. Exhalation of the Mucous Membranes.
The mucous membranes, like the skin, which they so strongly resemble in their structure, functions and diseases, exhale a similar transpiratory fluid; which has not, however, been subjected to chymical examination. It is, indeed, almost impracticable to separate it
from the follicular secretions, poured out from the same membrane; and from the extraneous substances, almost always in contact with it. It is probably, however, similar to the fluid of the cutaneous and pulmonary depurations, both in character and use.
Sect. II.—Follicular Secretions.
The follicular secretions must, of necessity, be effected from the skin or the mucous membranes; as the follicles or crypts are met with there only. They may, therefore, be divided into two classes:1st, the mucous follicular secretion; and 2d, the cutaneous follicular secretion.
1. Mucous Follicular Secretion.
The whole extent of the great mucous membranes, lining the alimentary canal, the air-passages and the urinary and genital organs, is the seat of a secretion, the product of which has received, in the abstract, the name of mucus; although it differs somewhat according to the situation and character of the particular follicles, whence it proceeds. Still, essentially, the structure, functions and product are the same.
In the history of the different functions, in which some of the mucous membranes are concerned, the uses of this secretion have been detailed; and in those that will hereafter have to engage attention, in which other mucous membranes are concerned, their uses will fall more conveniently under notice then. But few points will, therefore, require explanation at present.
The mucus, secreted by the nasal follicles, seems alone to have been subjected to chymical analysis. Fourcroy and Vauquelin found it composed of precisely the same ingredients as the tears. According to the analysis of Berzelius, its constituents are as follows: water, 933.7; mucus, 53.3; muriates of potassa and soda, 5.6; lactate of soda, with animal matter, 3.0; soda, 0.9; albumen and animal matter, soluble in water, but insoluble in alcohol, with a trace of phosphate of soda, 3.5.
The great use of mucus, wherever met with, is to lubricate the surface on which it is poured.
2. Follicular Secretion of the Skin.
This is the sebaceous and micaceous humour, observed in the skin of the cranium, and in that of the pavilion of the ear. It is also the humour, which occasionally gives the appearance of small worms beneath the skin of the face, when it is forced through the external aperture of the follicle; and which causes, when exposed to the air, the black spots sometimes observable on the face. The cerumen is, likewise, a follicular secretion, as well as the whit
ish, odorous and fatty matter, which forms under the prepuce of the male, and in the external parts of the female, where cleanliness is disregarded. The humour of Meibomius is also follicular, as well as that of the caruncula lachrymalis. The use of this secretion is, to favour the functions of the part over which it is distributed. That which is secreted from the skin, is spread over the epidermis, hair, &c., giving suppleness and elasticity to the parts, rendering the surface smooth and polished, and thus obviating the evils of abrasion that might otherwise arise. It is also conceived, that its unctuous nature may render the parts less permeable to humidity.
Sect. III. Glandular Secretions.
The glandular secretions are seven in number;—those of the tears, saliva, pancreatic juice, bile, urine, sperm, and milk.
1. Secretion of the Tears.
The lachrymal apparatus, being a part of that accessory to vision, was described under that head. As we meet with the tears, they are not simply the secretion of the lachrymal gland, but of the conjunctiva, and occasionally of the caruncula lachrymalis and follicles of Meibomius. They have a saline taste; mix freely with water; and, owing to the presence of free soda, communicate a green tint to the blue infusion of violets. Their chief salts are the muriate, and phosphate of soda. According to Fourcroy and Vauquelin, the animal matter of the tears is mucus; but it is presumed by some to be albumen or an analogous principle.
This secretion is more influenced by the emotions than any other; and hence it is concerned in the expressions of lively joy and sorrow, especially of the latter.
2. Secretion of the Saliva.
The salivary apparatus has, likewise, engaged attention elsewhere. It consists of a parotid gland on each side, situated in front of the ear and behind the neck and ramus of the jaw; a submaxillary, beneath the body of the bone; and a sublingual, situated immediately beneath the tongue,—the parotids and submaxillary glands having each but one excretory duct, the sublingual several.
All these ducts pour the fluids of their respective glands into the mouth, where it collects, and becomes mixed with the exhalation from the mucous membrane of the mouth, and the secretion from its follicles. It is this mixed fluid, that has been generally analyzed by the chymist.
According to Berzelius, its constituents are,—water, 992.2; pe
culiar animal matter, 2.9; mucus, 1.4; muriates of potassa and soda, 1.7; lactate of soda, and animal matter, 0.9; soda, 0.2. Drs. Bostock and Thomas Thomson think, that the "mucus" of Berzelius resembles coagulated albumen in its properties.
MM. Leuret and Lassaigne analyzed pure saliva, obtained from an individual labouring under salivary fistula, and found it to contain, water, mucus, traces of albumen, soda, chloride of potassium, chloride of sodium, carbonate and phosphate of lime ;—and lastly, Messrs. Tiedemann and Gmelin affirm, that the saliva contains only one or two-hundredths of solid matter, which are composed of a peculiar substance, called salivary matter; osmazome; mucus; perhaps albumen; a little fat, containing phosphorus; and the insoluble salts—phosphate and carbonate of lime. Besides these, they detected the following soluble salts;—acetate, carbonate, phosphate, sulphate, and muriate of potassa, and the sulpho-cyanate of potassa.
As the salivary secretion forms an important part in the processes preparatory to stomachal digestion, its uses have been detailed in the first volume of this work.
3. Secretion of the Pancreatic Juice.
The pancreas or sweatbread, Fig. 122, G., secretes a juice or humour, called succus pancreaticus or pancreatic juice. Its texture resembles that of the salivary glands; and hence it has been called, by some, the abdominal salivary gland. It is situated transversely in the abdomen, behind the stomach, towards the concavity of the duodenum; is about six inches long; of a reddishwhite colour, and firm consistence. Its excretory ducts terminate in one,—called the duct of Wirsung,—which opens into the duodenum, at times separately from the ductus communis choledochus, but close to it; at other times, being confounded with, or opening into, it.
The quantity of fluid, secreted by the pancreas, does not seem to be considerable. Magendie, in his experiments, was struck with the a. The hepatic duct, formed by a branch from the right, small quantity discharged. and one from the left lobe of the liver.-6. Fundus of gall bladder.-c. d. Body and neck of gall-bladder.-e. Cystic Frequently, scarcely a drop duct.-f. Ductus communis choledochus.-gg. Trunk and issued in hair an hour; and, ductus communis choledochus and the ductus pancreati branches of the pancreatic duct.-h. Termination of the occasionally, a much longer cus.-. The duodenum.
time elapsed. Nor did he find that the flow, according to the com
mon opinion and to probability, was more rapid whilst digestion was going on.
It will be easily understood, therefore, that it cannot be an easy task to collect it. De Graaf, a Dutch anatomist affirms, that he succeeded by introducing, into the intestinal end of the excretory duct, a small quill, terminating in a phial fixed under the belly of the animal. Magendie, however, states, that he tried this plan several times but without success; and he believes it to be impracticable. The plan he adopts is to expose the intestinal orifice of the duct; to wipe, with a fine cloth, the surrounding mucous membrane; and, as soon as a drop of the fluid oozes, to suck it up by means of a pipette or small glass tube. In this way he collected a few drops, but never sufficient to undertake a satisfactory analysis.
Messrs. Tiedemann and Gmelin make an incision into the abdomen; draw out the duodenum, and a part of the pancreas; and, opening the excretory duct, insert a tube into it; and a similar plan was adopted successfully on a horse by MM. Leuret and Lassaigne.
The difficulty experienced in collecting a due quantity, is a probable cause of some of the discrepancy amongst observers, regarding its sensible and chymical properties.
Some of the older physiologists affirm it to be acidulous and saline; others assert that it is alkaline.
The majority of those of the present day compare it to the saliva, and affirm it to be inodorous, insipid, viscid, limpid, and of a bluish white colour. The latest experimenters by no means accord with each other.
According to Magendie, it is of a slightly yellowish hue, saline taste, devoid of smell, occasionally alkaline, and partly coagulable by heat.
MM. Leuret and Lassaigne found that of the horse, of which they obtained three ounces, to be alkaline, and composed of 991 parts of water in 1000; of an animal matter, soluble in alcohol; another, soluble in water; traces of albumen and mucus; free soda; chloride of sodium; chloride of potassium, and phosphate of lime.
In their view, consequently, the pancreatic juice strongly resembles the saliva.
MM. Tiedemann and Gmelin succeeded in obtaining upwards of two drachms of the juice in four hours; and, in 100 parts, they found from five to eight solid. These solid parts consisted of osmazome; a matter which became red by chlorine; another analogous to caseine, and probably associated with salivary matter; much albumen; a little free acid, probably the acetic; the acetate, phosphate, and sulphate of soda, with a little potassa; chloride of potassium, and carbonate and phosphate of lime: so that, according to these gentlemen, the pancreatic juice differs from the saliva in containing;
a little free acid, whilst the saliva is alkaline; much albumen, and matter resembling caseine; but little mucus and salivary matter, and no sulpho-cyanate of potassa.