Is the nature of the blood changed when it arrives at the glands? Has it a peculiar composition before entering each of them? Much has been said of this change necessary to secretion; but that this may take place, there must be a cause to produce it; now what is this cause here? Does not the blood circulate in the trunks which go to the glands, as in the others? It would be necessary then that the gland should be surrounded with an atmosphere which acts upon the blood at a certain distance from the place where it is; a vague idea, which has no solid foundation, and which is met with only in the books of those who have never made experiments. I have drawn blood from the carotid, spermatic, hepatic and renal arteries; it is equally red and coagulable. In the same animal, it is impossible for the senses to discover the least difference.
I would observe that secretion differs essentially from nutrition in this, that it always draws the materials of its fluids from the red blood, whereas the second often takes its own from the white fluids, as we see in the tendons, the cartilages, the hair, &c.
Nerves.
The glands receive two species of nerves. 1st. The cerebral are found almost exclusively in the salivary and lachrymal glands, the amygdalæ, &c. 2d. The testicles, the prostate gland and the liver receive them in an almost equal proportion from the brain and the ganglions. 3d. The kidneys and most of the mucous glands receive scarcely any but those of the ganglions. What is now said of the nerves should be understood only of those that are free and independent of the arteries; for each arterial trunk that enters a gland, is surrounded by a nervous net-work belonging to the system of the ganglions, which is very evident in the great glands, as in the liver and the kidneys where this net-work comes from the semilunar ganglion, in the salivary glands where it comes from the superior cervical, in the testicles where it comes from the lumbar ganglions, &c.
Compared with the size of the glands, the nerves are in small proportion, notwithstanding what Bordeu has said. It is not necessary in fact to judge of this proportion by those of the parotid and sub-maxillary glands, which merely pass through these glands without stopping in them, and leave only some branches there. For example, there is certainly no organ in the economy, among those which receive nerves, that, in proportion to its size, has so few as the liver.
Besides, the nerves enter the glands nearly in the same way as the blood-vessels, that is to say, 1st, on all sides, in those that have no membrane; 2d, by a groove only in those that are covered with one. They divide and subdivide after entering it, and are soon lost sight of. Ganglions never exist in the interior of the glands.
Have the nerves an influence upon secretion? It is probable they have, as every gland is provided with them; but they by no means exert so immediate an influence upon this function as many physicians have pretended. 1st. It is said that the nerves of the parotid glands have been cut, and that the secretion of the saliva has been suppressed. This division is evidently impossible, since the gland must be extirpated before removing its nerves. 2d. I have divided the nerves of the testicle of a dog, the only gland in which this experiment can be made. I could not obtain any result, because an inflammation of the gland came on and it suppurated; but this suppuration even supposes that the nervous influx is not actually necessary for secretion, since suppuration is accomplished by a mechanism analogous to that of this function. All physicians know that a paralyzed limb can inflame and suppurate. 3d. Erection and the ejection of semen take place in paralysis of the lower half of the body, in which at least the nerves of the prostate gland are completely paralyzed. Mr. Ivan related to me the case of a soldier who took gonorrhœa in this state. 4th. We know that when the bladder is perfectly paralyzed and its nerves have no longer any action, its mucous glands still continue to secrete their fluid so as even to produce a catarrh. 5th. The nostril of the affected side in hemiplegia is as moist as usual. The ear of this side has its ordinary quantity of wax. 6th. In paralysis of the uvula, the action of its glands continues. 7th. When the eighth pair of one side of a dog is cut, the bronchia is found some days after to contain as much mucus as common. 8th. During the convulsions of the different parts in which there are glands, and when consequently the nerves of these glands are more excited, their secretion is not increased. 9th. If we weigh the proofs given by Bordeu of the influence of the nerves on secretions, we shall see, that they either rest upon false facts, like those of the section of the nerve, of sleep, &c. or upon vague data. In general physicians attach no precise idea to the term nervous influence; the habit of experimenting shows how much they have abused it. When a nerve being cut, paralyzed or irritated in any manner, the organ which receives it undergoes no derangement in its functions, we certainly are unable to appreciate the nervous influence upon this organ. I do not say that it does not exist, but I maintain that we know nothing about it, and that we ought not to employ at hazard a word to which we cannot attach any precise idea. What word will you employ then to express the influence of the nerves upon the organs of the senses, upon the voluntary muscles, &c. if the same one is used to express an action which has no relation with this, and which perhaps even does not exist?
Exhalants and Absorbents.
This kind of vessels is but little known in the interior of the glands, where they perform only the purposes of nutrition.