Section V. !
The most obvious use of the absorbent vessels is to convey the lymph and chyle into the venous system; the former is the residue of nutrition, and the latter the product of digestion. These fluids are not merely emptied into the great veins of the neck but likewise, as the observations offered at p. 315 sufficiently prove, into the veins of other parts of the body.
In the present day, the opinions of physiologists are divided as to the share which the lymphatics enjoy in the process of absorption. It has been generally believed since the time of the Hunters and Monro that these vessels are the only instruments employed in that function. In later years, the absorbing power of the lymphatics has been called into question; and many writers, particularly M. Magendie, have revived the ancient hypothesis of venous absorption. One of the most decisive experiments against the truth of the Hunterian doctrine was the following, which was performed on a dog previously made insensible by opium. The thigh was divided, with the exception of the femoral artery and vein; a quill was introduced into each vessel, and fixed there by two ligatures; the artery and vein were then divided between the threads, so that, in fact, the only connexion between the leg and the body of the animal was that established by the two quills, through which the circulation was maintained. Two grains of the upas tieute were then introduced into the foot, which produced the usual effects, and caused death in about four minutes.* This result seemed to prove that the veins had absorbed the poison, and so conveyed it into the body. But there is a serious objection to this and similar experiments; for as there are free communications between the small lymphatics and veins, it is probable that the poisonous substance was absorbed by the former, and subsequently carried into some of the venous branches below the ligature.* The functions of the lacteals are not much more accurately known than those of the common lymphatics. Some physiologists, as John Hunter and Blumchenbadi, contend, that they nut only absorb chyle, but also other substances, which are introduced into the intestines. This opinion was supported by some experiments performed by Hunter. He injected milk, and other coloured fluids, into portions of the small intestine, and, for a short time, these substances were distinctly seen in the lacteal tubes, but no part of them could be discovered in the mesenteric veins. The certainty and accuracy of these investigations have been doubted by some of the most distinguished physiologists of the present day. M. Magendie has made a great number of experiments from which he concludes the lacteals absorb chyle only, and that when any other substance is placed in the intestines, it is taken up by the veins. These ideas are strongly corroborated by the following experiment, which was performed by M. Sepilas. A portion of the small intestine was insidated from the adjoining intestine by two incisions; all the arteries and veins belonging to it were tied, but the lacteals were carefully excluded from the ligature. A watery solution of the alcoholic extract of nux vomica was then injected into the fold of intestine, where it was secured by two ligatures. None of the usual effects produced by the poison were observed during the space of an hour; but, on untjing one of the veins, the poisoning took place in six minutes.* In reflecting on the opposite results which were obtained by Hunter and Magendie in their researches, it must be confessed that our knowledge of the function of absorption is doubtful and unsatisfactory. The following, however, are the conclusions which appear to be warranted by the facts we possess: — I. The lymphatic vessels are the principal, if not the only, agents of absorption. 2. The intestinal vessels absorb the chyle, and probably other substances, introduced into the intestines. 3. Extraneous substances, which are artificially introduced into the internal parts of the body, soak through the various tissues, and, in this manner, find their way directly into the blood, through the coats of the blood-vessels. 4. It is probable that the veins take up the substances which are brought in contact with them, merely by this kind of imbibition, and that they do not absorb in the manner of the lymphatics.
The circulation in this system is slow, and generally uniform, but it is accelerated by external compression. Thus, if the thoracic duct be opened in a living animal, near its termination, it is found that the flow of the contained fluids is quickened whenever the abdomen is compressed, either by the action of the respiratory muscles, or by the hand of the observer.
The principal power which effects this circulation appears to be the contractility of the lymphatic and chyleferous vessels; but their innumerable valves, and the pressure of the surrounding parts, materially assist in the process. Atmospheric pressure, will be seen below, is also an agent which assists the absorbers in propelling their contents towards the heart.
We know but little of the cause which determines the various substances that are contained in the lymphatics and lacteals to enter those vessels in the first instance. This phenomenon has been attributed to capillary attraction — to the sensibility of the absorbing mouths, and to the organic contractility they are supposed to possess — to imbibition — and, lastly, to atmospheric pressure. These hypotheses have been respectively supported by numerous observations and experiments, but none of them are sufficiently conclusive to establish the fact of any one of the above agents being the whole cause of absorption.
Although the pressure of the atmosphere does not appear to be the efficient cause of absorption, yet it is certain that it exerts a great influence on that process; so that if it be removed from any part of the body, the absorbing tubes are no longer able to perform their office. This fact has been satisfactorily proved by the very important experiments of Dr. Barry. He found, that when the most active poisons, as the concentrated prussic acid, strychnine, and upas tieute, were introduced under the skin of living limbs, their absorption and consequent baleful effects, were entirely suspended by the application of a cupping-glass over the place where the poison was lodged. It was farther ascertained, that if the application of the glass was continued for half an hour, it prevented absorption during the hour or two immediately succeeding its removal; and also, that when the symptoms of poisoning became apparent, they were specially removed by the re-application of the cupping-glass.* These investigations are of great practical importance in the treatment of poisoned wounds. In such cases Dr. Barry recommends, that the cupping-glass should be applied for at least an hour; that the wounded or abraded part should then be freely excised, after which the glass should be re-applied in order to tempt any particles of the virus which may still remain; and lastly, that the actual cautery should be employed when thought necessary, as in the bite of a rabid animal, but never under any circumstances before the second application of the cupping-glass.*
<Callout type="important" title="Important">The lymphatic vessels are the principal agents of absorption and must not be overlooked.</Callout> The thoracic duct is an important part of this system, as it can significantly affect fluid flow in the body. <Callout type="risk" title="Risk">Improper use of cupping glasses can cause additional injury if not applied correctly.</Callout>
- See Experiments on Atmospheric Pressure, chap. iii. iv. and vi.
The glandular system is a separate topic that will be covered in the next section.
Key Takeaways
- The lymphatic vessels are crucial for conveying chyle and lymph into the venous system.
- The thoracic duct plays a significant role in fluid circulation, especially when compressed.
- Cupping glasses can be used to prevent or treat poisoning by interrupting absorption.
Practical Tips
- Understand that the lymphatic vessels are primary absorbers of chyle and other substances, which is critical for treating wounds and poisonings.
- Be aware of the thoracic duct's role in fluid dynamics; it can be compressed to slow down or stop the flow of fluids through the body.
- Use cupping glasses as a treatment method for poisoning by applying them over the affected area to prevent absorption.
Warnings & Risks
Warning
Improper use of cupping glasses can cause additional injury if not applied correctly.
- Do not apply cauterization before using cupping glasses, as it may worsen the condition.
- Be cautious when handling concentrated poisons like prussic acid or strychnine.
Modern Application
Understanding lymphatic and venous absorption is crucial for modern survival scenarios, especially in treating poisoning or managing injuries. While the techniques described here are historical, they provide a foundation for understanding fluid dynamics that can be applied to contemporary medical practices. Modern tools like syringes and antivenom have improved treatment methods but still rely on this fundamental knowledge.
Frequently Asked Questions
Q: What is the role of the thoracic duct in lymphatic absorption?
The thoracic duct plays a significant role in lymphatic absorption by conveying chyle and other fluids from the lower body into the venous system. It can be compressed to slow down or stop fluid flow, which is useful in certain medical treatments.
Q: How do cupping glasses work in treating poisoning?
Cupping glasses are used by applying them over the affected area to prevent the absorption of poisons. By creating a seal and removing atmospheric pressure, they can interrupt the process of absorption, thereby reducing the effects of toxins.
Q: What is the importance of understanding lymphatic vessels in treating wounds?
Understanding lymphatic vessels is important because they are primary absorbers of chyle and other substances. This knowledge helps in managing fluid dynamics during wound treatment, ensuring proper healing and preventing complications.