Section III. CHBHICAl, COMPOSITION.
It has been ascertained that the nervous substance is a peculiar chemical compound, unlike any other constituents of the body. The following is the analysis of the human brain, according to Vauquelin: Water 8000; Albumen 7.00; A white fat 453; A reddish brown fat .12; Osmazome 1.12; Phosphorus 150; Phosphates of potash, lime and magnesia, and soda 5.15.
The spinal cord and the nerves have the same constituent principles as the brain, but there is some slight difference in their proportions.
VITAL PROPERTIES. Section IV. PROPERTIES OR THE NERVOUS SYSTEM. The vital properties of the nervous system bestow on the animal kingdom a mode of existence which is totally wanting in plants; in virtue of these faculties every animal possesses: 1. A consciousness of its own existence. 2. A capability of receiving impressions from surrounding bodies. 3. A power of willing, by means of which it reacts on external objects. To these powers is super-added in the human species that of reason, which may be regarded in physiology as one of the functions of the brain, because it requires in our present state of existence the agency of that organ for its display.
Without entering into any examination of the comparative merits of this question, I may be permitted to express my perfect conviction, that if the investigation be conducted upon an anatomical and physiological basis, the materialists will fail in proving that the mental superiority of man is merely the result of the perfection displayed in his cerebral organization.
DIFFErent KINDS OF SENSIBILITY. All the nervous functions are generally supposed to spring from one great property, which is named sensibility; by this word physiologists express: 1. The power which the nervous system possesses of receiving and transmitting certain impressions and producing corresponding changes in the sensorium; 2. The power which the system enjoys of inducing the co-operative organs and in this manner of reacting on external objects. In the first operation, the impression passes from the circumference towards the centre of the system; in the second, the influence extends in the opposite direction, or from the centre towards the circumference.
It has just been stated that all impressions are not necessarily attended with consciousness; for this reason sensibility is divided into two species. In one kind the impression is not communicated to the mind; thus we are not conscious of the impression of the blood on the heart: in the other kind, the impression is transmitted to the mind; for example, we are aware of the contact of a foreign body with the finger. When an impression is thus perceived it constitutes a sensation or a perception.
The influence of organic sensibility, by which word I wish to express all the actions of the nervous system of which we are not conscious, on the vital functions of digestion, circulation, respiration, secretion, and on the production of animal temperature, has for a long time engaged the attention of physiologists. The subject has been particularly investigated by Mr. Brodie, M. Le Galloin, and Dr. L'hip. From the researches of these observers, we have obtained a variety of important information, but there are still many parts of this inquiry which remain involved in obscurity.
We learn from the experiments of Dr. Philip that the nervous influence is essential to digestion. This phenomenon appears to be suspended in consequence of the section of the gastric bulb being supplied by the destruction of the nervous power of the stomach. The effect of these experiments on the secreting power of the internal surface of the stomach, lends to the supposition that the process of secretion in general is connected with the nervous influence and cannot be performed without its interregation. Although this deduction is probably correct, at least in the higher classes of animals, it must be known that the observations on which it is founded are not sufficiently extensive to warrant us in deducing entirely in the affirmative.
The contractile power of the various structures which circulate the blood, is independent of the nervous system; but, as we have already seen, the heart and the blood-vessels are capable of being excited by the nervous power. The influence of the par vagus upon the functions of the lungs has been known for a considerable time; it is, however, only lately that the precise effects resulting from the loss of the nervous power of the pulmonary organs have been ascertained. The division of the cord or the description of a considerable part of the spinal cord, causes an accumulation of frothy mucus in the bronchial tubes and air-cells, and a congestion of the blood-vessels of the lungs. The consequence of this obstruction is that a smaller volume of air than natural is admitted, and that the blood contained in the pulmonary vessels cannot be brought in contact with the air, so as to undergo the necessary changes. In these cases the animal is deprived by a process exactly similar to suffocation, except that it is less complete, and consequently less rapid in its progress.
One of the most important functions of the animal economy is that, by which the body is capable of resisting, to a certain extent, the changes of external temperature, and of preserving, more or less, an uniform degree of heat. It appears that the production of animal heat is connected with certain chemical combinations which occur in the process of respiration; but it has also been proved by the experiments of Mr. Brodie and others, that the nervous power is essential to the evolution of caloric.
The preceding observations are offered merely as a sketch of the important connexions that exist between the nervous power and those organs which exercise functions essential to the support of life. The actions of the nervous system, which are attended with consciousness, produce more striking effects than those depending upon organic sensibility. They consist, in the human species, of — I. Sensation. 3. Volition. 3. The intellectual faculties.
Of Sensation. When an impression made upon an organ of the body by a physical agent is transmitted to the brain, it produces a tension; thus, when the vibrations of the atmosphere act on the nerve of hearing, we experience the sensation of sound. The sensations require to be divided into two opposite, according the cause that makes the impression, is external or internal. The external senses are five in number; vision, hearing, touch, taste, and smell. The number of the internal senses has not been satisfactorily determined. The sensations of hunger and thirst, and those which attend the actions of the muscles and of the genital organs, appear to belong to this class. Many physiologists believe that the power by which we are enabled to estimate the effects of temperature on our frame, should be regarded as a separate sense. Other writers, however, consider this power to be merely a modification of that function of the cutaneous organ, which is called tact.
In the exercise of the senses three conditions are necessary: 1. The impression of the physical agent upon the extremity of the appropriate nerve; 2. The transmission of that impression by the trunk of the nerve to the sensorium; 3. The perception of the impression by the mind. If any one of these conditions be wanting, no sensation can be experienced.
The impression which is made upon an organ of sense is not perceived in the organ itself, but in the brain. It is true, indeed, if the feelings alone were relied on, we should conclude that the sensation is experienced in the organ, because we refer the perception to the part which receives the impression; thus the influence of light is felt in the eye, and the contact of a foreign body in the part of the skin which it touches. But experiment and observation inform us, that sensation resides in the brain; for if the communication be cut off between it and an organ of sense, no impression made upon that organ is perceived.
Volition may be considered, in its general signification, as a modification of desire, resulting from painful or pleasurable impressions which have been perceived by the mind. But in a physiological sense, volition is used to express the stimulus by which the class of voluntary muscles is excited to action. In the exercise of this power, the influence, whatever it may be, is transmitted through a peculiar set of nerves from the centre towards the extremity of the nervous system.
Of the Intellectual Faculties. I shall not enter into the enumeration of the various phenomena which constitute the human intellect; because it would be impossible to do so without discussing the method according to which they should be considered. Such an investigation would lead to details foreign to the object of this work, since almost every author who has confuted this abstruse subject, has given a different account of the mental faculties.
The source of the mysterious power, which operates through the medium of the nervous system, is entirely unknown; we are compelled ignorant of the manner in which this power acts on the material organs, the brain and the nerves, that are essential to the manifestation of its phenomena. The deficiency in our information has not resulted from any want of inquiry, for this question but at intervals commanded an intense interest amongst philosophers. I shall only notice in this place the most modern, and at the same time the most plausible of the numerous theories which have been invented to remove the difficulty.
It has been supposed by many eminent physiologists, amongst whom it will suffice to mention Curier, Alavernethy, and W. Philip, that the power by which the nerves transmit impressions to and from the brain is analogous to, or even identical with electricity. This hypothesis is strongly supported by the facts, that when it is in perfect division, its action may be imitated by galvanic electricity; thus, after the section of the par vagus, the secreting power of the lungs and stomach can be supported by galvanism. The evolution of heat from the blood, can (dwi) be accomplished by the same power; and it is well known that muscular contraction is capable of being excited by the agency of galvanism. It is likewise worthy of remark, that when the par vagus in dimply divided, the nervous power is still transmitted to the stomach; and even when the two ends are severed to the extent of a quarter of an inch, a part of the nervous power is conveyed from the upper to the lower portion of the nerve. These instances mentioned phenomena are very limited to those produced by electricity; and tend, in a very forcible manner, to show the identity of the nervous and galvanic powers. But in establishing a doctrine of such importance, further evidence is required, and therefore it will be prudent, in the present state of the question, to defer forming any definitive conclusion.
<Callout type="important" title="Critical Observation">The division of the par vagus can lead to severe respiratory issues, similar to suffocation.</Callout> <Callout type="risk" title="Galvanic Power Risks">While galvanism can mimic nervous functions, it poses significant risks and should be approached with caution in survival scenarios.</Callout>
Key Takeaways
- The human brain is composed of water, albumen, fats, osmazome, phosphorus, and various salts.
- Sensation and volition are vital properties of the nervous system that enable animals to react to their environment.
- The par vagus nerve plays a crucial role in regulating lung functions and can lead to severe consequences if damaged.
Practical Tips
- Understand the critical importance of the brain and nerves for survival, as they control essential bodily functions like digestion and temperature regulation.
- Be cautious when dealing with galvanic electricity; it can mimic nervous functions but poses significant risks in practical applications.
- Recognize that sensation is processed in the brain rather than at the site of physical contact.
Warnings & Risks
- Do not underestimate the potential dangers associated with the division or severing of nerves, as it can lead to severe physiological issues.
- Avoid experimenting with galvanism for survival purposes without proper knowledge and equipment; it can be dangerous.
Modern Application
While the historical techniques in this chapter provide foundational understanding of the nervous system, modern survival preparedness emphasizes more practical applications such as first aid, emergency medical procedures, and environmental adaptation. Understanding these principles can still inform effective response strategies during crises.
Frequently Asked Questions
Q: What is the composition of the human brain according to Vauquelin?
According to Vauquelin, the human brain consists of water (8000), albumen (7.00), white fat (453), reddish brown fat (.12), osmazome (1.12), phosphorus (150), and various salts including phosphates of potash, lime, and magnesia, as well as soda (5.15).
Q: How does the par vagus nerve affect lung functions?
The par vagus nerve is crucial for regulating lung functions; its division can cause an accumulation of frothy mucus in the bronchial tubes and air-cells, leading to a smaller volume of air being admitted into the lungs. This can result in a process similar to suffocation.
Q: What role does galvanism play in understanding nervous functions?
Galvanism is used as an analogy for the nervous system's power; experiments show that after the section of the par vagus, its actions can be imitated by galvanic electricity. This helps to understand how the nervous system operates but should be approached with caution due to potential risks.