cally to expel their contents. Thus, in the above cases, in addition to the failure of nervous influence in the viscera, there is a failure of excitement in the muscles of voluntary motion which conspire with these viscera in certain parts of their functions.

We can trace the communication of nerves issuing from the great chain of ganglions, placed it would seem, to facilitate these communications in the centre of the animal system, with all the nerves of the body. Bichat, although his opinions respecting the use of the ganglions are inconsistent with the results of the experiments just refer- . red to, as well as of others to which I shall have occasion to refer, was induced, from their situation and the distribution of their nerves, to regard them as the centres of nervous systems.

On comparing all the facts on the subject, we have reason to believe, that the system of ganglionic nerves is quite as extensive as that of the nerves proceeding directly from the brain and spinal marrow. We every where find blood vessels which, being influenced equally through the brain and spinal marrow, must receive the nervous influence through the ganglions; and, indeed we can trace the ganglionic nerves attached to and supplying the larger vessels. The following case, related by Dr. Parry, in his treatise on the arterial pulse, might alone be regarded as proving the existence of two sets of nerves in the extremities, the one supplying the organs of voluntary, the other those of involuntary, motion, and strikingly illustrates what has been said on this subject. He observes, “ I have seen a total loss of pulse in one arm, with coldness, but complete power of motion in that part while the other arm was warm, and possessed a perfectly good pulse, but had lost all power of voluntary motion.”

Such then is the manner in which the influence of the nervous system is supplied to the muscles of voluntary and involuntary motion. To the former, from certain small portions of the brain and spinal marrow, and through nerves going directly from these small portions to the muscles; to the latter, from every part of the brain and spinal marrow through a chain of ganglions which, on the one hand, communicate with every part of these organs, and, on the other, with all the muscles of involuntary motion; in the former instance, the influence of the nervous system being the only natural stimulus, in the latter, other stimuli exciting the muscle to its usual function, and the influence of the nervous system, being only occasionally bestowed on it for purposes which we shall soon have occasion to consider.

When the nerves of a muscle of voluntary motion are divided, the supply of the stimulus on which its function depends being cut off, it is rendered paralytic, not because its power is impaired, for it is as sensible to the effects of stimuli as while its nerves were entire, but because the channel of the only stimulus by which the will operates on it is obstructed, and here the effect of the division of these nerves ends. The consequence is very different, when the nerves of the muscles of involuntary motion, the ganglionic, are divided.

If the principal ganglionic nerves, the eighth pair through which the influence of the brain is chiefly supplied to those muscles be divided, the function of the muscles appears to be wholly unaffected by it. The heart and vessels support the circulation as well as before the division of the nerves. For this result we are prepared by what has been said of these muscles. An evident disorder, however, in the secreting

power of some of the vital organs immediately ensues. The stomach no longer secretes a fluid capable of producing the necessary change on the food, while the fluids of the lungs deviate from the healthy state, and accumulate in the bronchiæ and air cells. The structure of the lungs itself, in the space of a few hours, becomes evidently diseased, and the animal dies of dyspncea; failure in the office of the lungs, necessarily proving more suddenly fatal than failure in that of the

stomach. It has been questioned, whether the effects on secreting sur• faces of dividing the eighth pair of nerves should be ascribed to the

interruption of the influence of the brain, or to the injury done to those surfaces by the act of dividing their nerves. That it produces its effects in the former of these ways, appears from the following facts. When secreting surfaces are deprived of their nervous influence by any other means, the effect is the same; this effect is not at all proportioned to the degree of injury done to the nerves, but to the degree in which the nervous influence is withdrawn; and, as soon as the nervous influence is restored, the surface is again capable of its function. These facts seem sufficient to have answered the question, although it had not been determined by some late experiments, in which Mr. Brodie and Mr. Cutler were so good as to assist me, that it is necessary, after the division of the nerves, to displace one of the divided ends, in order wholly to arrest the function of the secreting surface, the influence of the brain still passing in such a quantity, if this be not done, as to bestow on that surface a considerable degree of the secreting power; and that even when the divided ends, if not otherwise displaced, are separated to a distance of a quarter of an inch,

Thus, we find, that the effect of dividing the ganglionic nerves is of a nature wholly different from that of dividing the cerebral, or spinal nerves; while the division of the latter only deprives the animal of the power of exciting the muscles of voluntary motion, that of the former deranges the functions on which its life depends. Even the structure of the lungs, we have just seen, is evidently disordered in a few hours by the division of the eighth pair of nerves in the neck.

As the function of the stomach is destroyed when the influence of the brain through the eighth pair of nerves iš cut off, we should at first view infer, that it is from the brain alone that the stomach derives its nervous influence. But although the process of digestion be suspended by the division of these nerves, it does not follow that the stomach may not derive nervous influence from some other source, because the loss of any considerable part of this influence may destroy its function. Besides, its remaining sensibility, indicated by the efforts to vomit, proves that the influence of the nervous system is not wholly withdrawn from it by dividing these nerves.

If, then, this influence be not supplied to the stomach by the eighth pair of nerves alone, but also, as we have reason to believe from the evidence of anatomy, by nerves arising from different parts of the spinal marrow, it is evident that cutting off the influence of any considerable part of this organ, while we leave the eighth pair of nerves entire, must affect the power of the stomach, though probably not so much, because the brain, we have reason to believe, constitutes the most important part of the nervous system. The same observation applies to the lungs. On appealing to the test of experiment, such was found to be the recult; the functions both of the stomach and lungs were impaired, by destroying any considerable portion of the spinal marrow, the lesion of function being proportioned to the extent and importance of the part destroyed.

Another point relating to this part of the subject remains to be ascertained. Do the effects observed in the stomach and lungs, when part of the spinal marrow is destroyed, arise directly from the destruction of that part, that is, from the ceasing of its office, or from the influence of the brain on the spinal marrow being thus limited ? It is evident, that if the former opinion be correct, the division of the spinal marrow in the middle will not produce the same effects as the destruction of the lower half. If the latter, the effects must be the same. The division of the spinal marrow in the middle produced very little deviation from the healthy state, either in the stomach or lungs, compared with that produced by the destruction of the lower half

of that organ.

Thus, it appears, that the function of the spinal marrow also is necessary to the secreting power, and that, as far as it is necessary to this power, it is independent of any influence derived from the brain. As a partial destruction of the spinal marrow impairs the secreting power, a partial abstraction of the influence of the brain has the same effect. It was found that the division of one of the eighth pair of nerves deranges the function of both the stomach and lungs, nearly in the same degree with the destruction of a certain portion of the spinal marrow. The function of every part of the brain and spinal marrow therefore is necessary to the due performance of secretion.

Here a question of great importance in the animal economy arises. As it appears, from the experiments just referred to, that the nervous power is equally essential with the circulation of the blood, for maintaining the functions of secretion and assimilation, what are the parts they severally perform in these functions? It is evident, that the extreme parts of the sanguiferous and nervous systems are connected in a way very different from that in which these systems are connected in other parts. The heart and vessels of circulation, we have seen, can perform their functions after the influence of the nervous system is withdrawn. The function of the secreting vessels immediately ceases on the interruption of this influence. We must suppose, therefore, either that the influence of the nervous system bestows on the extreme vessels the power of separating and recombining the elementary parts of the blood, or that the vessels only convey the fluids to be operated upon by this influence.

Experiments, to which I have already referred, prove that the most minute vessels which can be seen by a powerful microscope in the web of a frog's foot, are independent of the nervous system. The motion of the blood is as rapid, and the circulation in the foot presents precisely the same appearance after as before the slow destruction of the brain and spinal marrow. If the power of the vessels of secretion had been lost by the interruption of the influence of the nervous system, would not this have necessarily occasioned some change in the distribution and motion of the blood in the web? The conclusion from these experiments is strengthened by others. In those in which the secreting power was destroyed either by the division of the eighth pair of nerves or the destruction of part of the spinal marrow, there Vol. I. Ne. Museitm.

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did not necessarily appear to be a defective supply of fluids. In the stomach they were often as copious, sometimes more copious, than usual ; and the latter was almost always the case in the lungs. The fault seemed to be, that a due change on them had not been effected. We know that the vessels of circulation possess no powers but the elastic and the muscular, or what in many of its properties resembles the latter. Can we suppose, that the vessels of secretion, which are only a continuation of those of circulation, all at once assume a different nature; or is it at all consistent with our knowledge of the phenomena of chemistry to suppose, that by any influence the powers just mentioned, or indeed any that can be supposed to belong to vessels, could be enabled to separate and re-combine the elementary parts of the blood ? The first of the above positions being set aside, it seems a necessary inference from the experiments referred to, that in the function of secretion, the vessels only convey the fluids to be operated upon by the influence of the nervous system.

It is not to be overlooked, however, that the vessels convey the fluids in a peculiar way. By the lessening capacities of the capillaries, the blood is divided, as by a fine strainer, some of its parts being too gross to enter the smaller vessels. How far the blood may thus be ; subdivided we cannot tell. As this structure of the vessels is uniform, we have reason to believe, that its effect on the blood is necessary to prepare it for the due action of the nervous influence.

We are now prepared to consider the question, for what purpose is the influence of the whole nervous system bestowed on the muscles of involuntary motion ? Admitting, it may be said, that the due performance of secretion requires the united power of all parts of the brain and spinal marrow, and that we may therefore explain why their united influence is bestowed on secreting surfaces; the question still remains, why should their united influence be bestowed also on the muscles of involuntary motion ?

It is evident, that affections of the nervous system could produce no occasional increase of the secretions, were not the sanguiferous system, and particularly the vessels of secretion, capable of being stimulated by the same influence which operates in the formation of the secreted fluids. The increase of secreting power in any part would be in vain, were there not at the same time a corresponding increase in the supply of the fluids on which it operates. A similar observation applies to the excretory muscles, as far as they are muscles of involuntary motion. The same increase of nervous influence which occasions an increased flow of secreted fluids, excites these muscles to carry off the increased quantity. Nature does not seem to trust this to the increase of stimulus, occasioned by the increased flow of the secreted fluid, which we have reason to believe from the modus operandi of certain causes of inflammation, would often occasion morbid distention. Now the vascular system, and the muscles of excretion, if in them we include the alimentary canal, comprehend all the muscles which are supplied with ganglionic nerves, unless we regard the iris as a muscle. The state of this organ is quite anomalous in the animal economy, being one of involuntary motions, excited only through the medium of the nervous system.

In the preceding view of the subject, we find the relation of the

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vessels of secretion to the nervous system the same as that of the heart and vessels of circulation. Their function is independent of, but capable of being influenced by, this system.

Thus, we perceive, the necessity of every part of the function which the ganglions appear to perform. A combination of the whole nervous influence is necessary to the due formation of the secreted fluids; and that there may be, under all circumstances, both a due supply of the fluids to be acted upon, and a due removal of those prepared, whether for the functions of life, or for the purpose of being thrown out of the system, it is necessary, as appears from what has just been said, that the powers which convey all these fluids should be subjected to the influence by which secretion is performed. This function, it is evident, requires a more regular supply of fluids than could have been obtained, had the usual action of the vessels depended on the nervous system, which is subject to continual variation ; but had not this system been capable of influencing the vessels, not only no change in it could have influenced the flow of secreted fluids, but

every

occasional increase of the influence of the nervous system, supplied to secreting surfaces, finding no increase of fluids to act upon, would necessarily have excited disease. Thus, it is requisite that the power of the sanguiferous should be independent of the nervous system, yet capable of being influenced by it; as from direct experiment, we have just seen, it is found to be.

The secreting processes are constantly attended with a temperature considerably raised above that of the surrounding medium. Does this also depend on a function of the nervous system?

It appears, from experiments above referred to, that the destruction of any considerable portion of the spinal marrow, deranges the function of secreting surfaces. Together with this effect, it was always found to lessen the temperature

of the animal, more or less, according to the extent and importance of the part destroyed. Some years previously, Mr. Brodie, in the Croonian Lecture for 1810, gave an account of experiments which led to the inference, that the maintenance of animal temperature is under the influence of the nervous system, and in the Philosophical Transactions of 1812, he relates additional experiments, tending to strengthen this inference. The experiments related in the inquiry just referred to, seem in a striking manner to confirm the opinion of Mr. Brodie. He found that poisons impairing the vigour of the nervous system, impair the temperature. It appears from my experiments, that lessening the extent of this system, by destroying part of the spinal marrow, has the same effect.

Thus, it follows, that the temperature of the animal body depends on the state of the nervous system; but many observations point out that it depends also on that of the powers of circulation. When the power of the heart and vessels is greatly impaired, so that the motion of the blood languishes, the temperature falls. If by exercise, or the use of stimulants, we increase the action of the heart and vessels, the temperature in the same proportion rises. When there is a natural defect in the organs of circulation, and particularly when this defect is such as prevents the blood passing through the lungs, with the freedom necessary to its healthy state, the temperature is found below the natural standard. The reader may consult a paper on this subject, by Mr. Earle, in the seventh volume of the transactions of the Medico