ON THE LAW OF ASSOCIATION BETWEEN SENTIENT AND MOTOR NERVES

I. Pidduck
1845 The Lancet  
613 figure. According to Hewson, Young, Hodgkin, Lister, and Queckett, their form is that of biconcave lens-a vesicle or cell, with thickened walls, in a collapsed condition ; the coverings of the cells admit of transudation, and by the addition of water to blood, endosmosis takes place, and the corpuscles acquire the form of a distended cell, with thinned coats, and become so transparent as to be with difficulty perceived. Red corpuscles thus changed may be brought back to their original form,
more » ... more or less, by the action of re-agents which are capable of inducing exosmosis. The enveloping cell is composed of a peculiar protein compound, closely allied to albumen, globulin of Berzelius, which is left in combination with sulphuric acid, by the action of that acid on coagulum; whilst the internal coloured portion is haematosine, already sufficiently examined for our purpose. When chlorine is passed through an albuminous fluid, chlorite of protein is formed, and precipitated in white flakes; by the action of ammonia on this compound, a new oxide of protein, mixed with hydrochlorate of ammonia, is produced; this is tritoxide of protein, (gelatin of Bouchardat ;) it is also formed when fibrin or albumen is boiled in water. It is prepared in the lungs, and is consequently found in the blood, particularly in excited states of the system, as a main ingredient of the buffy coat. By dissolving this compound in potassa, and precipitating by an acid a second oxide, the binoxide (epidermose of Bouchardat,) is produced ; this oxide is insoluble in water, while the former is soluble. It is probable that both these oxides are formed from the fibrin as often as the blood passes through the lungs; this is demonstrated by an experiment of Scherer: he found, by exposure of moist fibrin to oxygen, that the gas was absorbed, and carbonic acid given out, but that more of the former disappeared than was accounted for in the evolution of the latter; the loss he found to be expended in the formation of an oxycompound of protein ; for the fibrin, after this exposure, on being boiled in water, left binoxide of protein undissolved, while the tritoxide was found in solution. Valentin and Brunner show that hourly 69 0575 grs. of oxygen are absorbed, which are not employed in forming the carbonic acid of the expired air. Mulder avails himself of most of these facts, (many of them his own discoveries,) in explaining the changes produced in the lungs by respiration. He presumes the bright red arterial blood corpuscles to be biconcave lenses, and therefore in a good condition to reflect a great amount of light; this concave form is in several ways materially influenced by the formation of oxyprotein taking place in the lungs; the contraction which will necessarily follow the formation of this " buffy" membrane, while the investing membrane being thus (as Emmert and Mayer have remarked) denser, whiter, and thicker, and consequently more opaque, will put them in a state more favourable to reflection, and necessarily heighten the colour. On reaching the systemic capillaries, the layer of oxidized protein is removed and decomposed, the protein being employed to repair the various struc-tures, while as to the oxygen, we may adopt Liebig's opinion that it "serves to produce change of matter, and determines the separation of living parts, and their conversion into lifeless compounds, as well as the formation of the secretions and excretions." Deprived in this manner of their envelopes, the arterial become venous corpuscles, the light passes more readily through their coats, and is materially altered from the change they have undergone from the double concave to the double convex form. Thus, then, the action of air on oxygen, or venous blood, is imputed to the absorption of the gas, not by the colouring matter, but by the protein, which is in consequence oxidized. Any agent which affects the form of the globules, and as a necessary result, at the same time, their reflecting power, in a corresponding degree alters their tint; for example, saline solutions produce exosmosis in venous blood. A consequence of this emptying is a collapsed condition, or concave form ; and the arterial hue, for reasons previously stated, is assumed ; while, on the other hand, washing this blood with water, or passing through it many gases, or treating it with dilute acids, induce endosmosis, and with this alteration of physical character is produced the venous colour. Doubtless the action of carbonic acid and dilute acids may be referred to the solution of oxy-protein; an alkaline fluid, in destroying the red colour, operates in a similar manner. Scherer is inclined to hold much the same opinion as Mulder, that the difference of colour between arterial and venous blood depends rather on physical than chemical causes, and by his experiments tends to confirm similar views of Henle and Nasse. A quantity of fresh and bright-red blood was mixed with water; it became dark, in fact venous ; and with the change of colour consequent on this dilution, the globules were found to have undergone a material physical alteration; they had lost their concave form, and had become spherical from the absorption of Water by their coats. Neutral salts added to blood thus darkened changes the form and colour of the corpuscles. The microscope shows that while carbonic acid causes the corpuscles to become spherical, oxygen reduces them to a hollowed form; in this case, doubtless, the mechanical action of the substance as a gas being interfered with by the chemical property it possesses in the formation of oxy-protein. If, through the mixture of blood and water previously spoken of, oxygen is transmitted, the dark colour still remains, in all probability on account of the absence of the necessary conditions for the formation of the firm covering; but if to it white particles, capable of reflecting light, as oil, milk, finely-powdered chalk, &c., are added, then the arterial hue is assumed. The conclusions that Scherer draws from these and other experiments are, that as the addition of distilled water cannot deoxidate the colouring matter, while neutral salts cannot add oxygen to it, and the actual addition of that gas does not produce a red colour in the blood, the change produced in the colour cannot be a chemical one. If the act of respiration in the living body, and addition of neutral salts out of it, produce the same change in the colour of the hematosine, it is possible that they both exert the same physical action as the envelopes of the blood corpuscles. Thus, then, the opinions of both Mulder and Scherer are essentially identical, and account, in a satisfactory manner, for the phenomena of respiration; both agree in referring the whole to the different refraction and reflection of light produced by the several forms of the corpuscles assumed under certain conditions ; Mulder considering that the change of form affords a sufficient explanation; Scherer, from his experiments, though he does not appear to deny the important part that form has to do with the change of colour, seems to think that the red tint depends additionally on the presence of white reflecting particles in the blood-in fact, chyle globules. IN replying to this question, proposed by Mr. Stephens, of Bristol, the brain will be viewed as a whole, and the nerves as simple uniform cords of intercommunication between the brain and all parts of the body. The spinal cord will be considered as a prolongation of the brain; not as made up of separate parts, but consisting of one organ, composed of cortical and medullary substance. It is not proposed to lay aside the distinction between nerves of special sense, of sensation, of respiration, and of motion, but to regard the nervous cords as uniform in their structure. Their difference in function will be regarded as arising not only from the particular portion of the brain or spinal cord, from which they originate, but from the difference in the mode of termination, and the structure of the organs on which they are expanded. The olfactory nerve, for instance, expanded on the nasal cavities, is sensible to the stimulus of odours; the optic nerve expanded into the retina is sensible to the stimulus of light; the auditory nerve expanded upon the cochlea and semicircular canals is sensible to the stimulus of sounds; the fifth pair, terminating in the teeth and cutaneous papillse, is sensible to objects of touch; the portio dura of the seventh pair, terminating in muscular fibres, is conducive to muscular motion; and so of the third and fourth. But for any appreciable difference in the nerves themselves, it might be safely inferred, that if the olfactory, the optic, or the auditory nerve, had been distributed to the skin, they would have been nerves of common sensation, instead of being nerves of special sense; or if they had terminated in muscular structure,
doi:10.1016/s0140-6736(02)64995-5 fatcat:u563krnf5rep7oqkca3j322sxu