On the use of the ophthalmoscope as a help to diagnosis in diseases of the nervous system / by John Ogle.

  • Ogle, John W. (John William), 1824-1905.
Date:
1860
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Licence: Public Domain Mark

Credit: On the use of the ophthalmoscope as a help to diagnosis in diseases of the nervous system / by John Ogle. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    BERNARD ON EXPERIMENTAL1 PATHOLOGY. Among the innumerable agents which possess the power of destroying life, there exist an immense number, which the Medical philosopher cannot, by any means, consider as diseases: no one, for instance, would think for a moment of giving that name to the bullet which slays the soldier in battle, or the thunderbolt which strikes the ploughman dead in the fields ; the same, of course, might be said of all the various causes of violent death; now, reasoning by analogy, miffht we not place a large number of so-called diseases in the same class ? A tumour which, by its situation, compresses the windpipe, and gradually increasing in size, superinduces suffocation at last; a stricture of the oesophagus, which prevents the passage of food into the stomach, and ultimately starves the patient to death; are not these mechanical obstructions, which, acting as impediments to some of the more important functions of life, gradually bring on death, by a slow, but inevitable process ? It would, of course, be superfluous to adduce other instances to the same purpose, but we are supported by the authority of Professors Trousseau and Pidoux, in assimilating to such cases those valvular affections of the heart, which, by constantly opposing the natural course of the blood, sooner or later produce a complete stasis of the circulation. The word disease, must, therefore, be understood to signify disorders of a more extensive nature, the existence of which is revealed by phenomena of an entirely general character. Such, however, are frequently the results of local affections ; the fact is established by daily experience; and we need only allude to the well-known effects of wounds and sores, in order to convince you that local causes frequently become the starting-point of general diseases. The results of our physiological experiments are, in this respect, perfectly in accordance with clinical observa- tion ; let, for instance, a poison be introduced under an animal’s skin; its action, during the first few moments, is entirely confined to a single point, but within a given space of time, its effects are felt throughout the living frame ; in what manner can similar facts be best explained? Such is the problem, the solution of which we are about to seek ; the difficulty, as you perceive, has been distinctly stated. _ That poisonous substances cannot act upon the tissues which compose the body, without having previously been absorbed, is perfectly clear ; but when, under their influence, general phenomena are produced, the vessels or nerves must evidently have been called into play; the vascular and nervous systems alone, as you are well aware, are distributed throughout the body in one unbroken chain ; andphysiology,in this case, abundantly confirms the inferences drawn from our knowledge of anatomy. The well-known experiments of Magendie have shown that after injecting into the arteries of a lrmb any given toxic substance, its ordinary effects may be indefinitely suspended, by tying the veins which connect the diseased part with the remainder of the economy. The animal’s life might, in this maimer, be almost indefinitely pro- longed ; but as soon as the vessels are untied, the poison flows into the torrent of circulation, and gives rise, as usual, to a series of phenomena which end in death. The fact is well known to the inhabitants of tropical countries, who, when bitten by venomous serpents, immediately apply a close liga- ture over the limb, in order to prevent the passage of the venom into the blood until proper remedies have been applied. , . . But the vessels which convey into the depth of our tissues both poisonous substances and the ordinary elements of nutrition, belong, as you are perfectly aware, to the arterial system; on the other hand, all foreign bodies which pass into the blood through the process of absorption are conveyed into the arterial circulation by the veins: we thus discover that when general symptoms have been produced in this manner, the two great divisions of the vascular system have both been called into play. It sometimes occurs, however, that the noxious principle which circulates in the veins, is eliminated during its passage; such, for instance, is the case with sulphuretted hydrogen, one of the most dangerous substances we are acquainted with : when injected into the veins, it escapes from the lungs, and is, in this manner, prevented from passing into the arterial current; and the animal, in consequence, does not experience the slightest injury from the operation, the poison having been expelled before it could reach the tissues, which its contact would have disorganized. The venous, or absorbent system, is therefore that part of the vascular network which con- tributes to the production of general phenomena, when deleterious agents are introduced into the economy; nor do the arteries begin to play their part before the veins have accom- plished theirs. But, as we have just stated, the poison is sometimes expelled before reaching the left side of the heart; and this elimination takes place on various points; but the pulmonary apparatus is the ordinary seat of the process. For this very reason, the inner coat of the lungs is perhaps the most powerful of all absorbent surfaces ; and poisons, when directly brought to bear upon it, produce a more instantaneous effect than when deposited upon any other point; introduced, as it were, into the very centre of the arterial system, they pass at once into the circulation without any possibility of being expelled. Thus sulphuretted hydrogen, when intro- duced into the lungs, extinguishes life within a few seconds ; while the same gas exists, to a considerable amount, in various parts of the intestinal tube, and even circulates in the veins, without producing the slightest inconvenience. It must, of course, be understood that the presence of poisons within the animal economy is perfectly innocuous as long as they are not collected together in sufficiently large quantities at a given moment. Small doses of the most dangerous sub- stances may be successively poured into the vessels, at distant intervals, with perfect impunity. In estimating the noxious power of toxic bodies, the amount actually contained within the blood must alone lie taken into consideration. But another channel exists, through which the power of these agents is enabled to make itself felt throughout the entire economy ; we allude, of course, to the nervous system. The essential difference which distinguishes sensitive from motor branches, has been carefully laid down in our preceding Lecture. The recurrent fibres, created for the purpose of transmitting to the central parts the im- pressions generated towards the surface of the body, are equally endowed with the property of communicating morbid impulsions to the entire economy ; experimental proofs are not wanting to establish this fact. On one occasion, we injected fine particles of sand into the femoral artery of a dog ; they reached of course the capillary vessels, and filled them up, so as to arrest the progress of the blood. An acute sensation of pain made its appearance, and a powerful reaction soon took place ; yet in this case the venous system had not been interfered with, the passage of sand into the capillaries being utterly impossible. We therefore see that in this case, fever, loss of appetite, general uneasiness, and other physiological effects, were produced exclusively under the influence of the nervous system ; and another experiment renders the demonstration still more forcible. When the anterior roots connected with the diseased limb have been divided, a complete paralysis of motion is the natural result; but sensation being entirely preserved, the pain is felt as before, and its consequences remain exactly the same. Let, on the contrary, the posterior roots be divided; and all general symptoms will at once disappear ; motion of course remains, but pain no longer exists ; and symptoms of a purely local character, such as a partial swelling of the limb, a certain degree of refrigeration, and other signs of arrested circulation, are the only phenomena observed. When the sensitive nerves have been preserved, the intensity of the febrile reaction which, takes place is sometimes so powerful as to produce death. . Local affections are therefore totally distinct in themselves from real diseases ; and, when _ they become general, the morbid impulse has been communicated to the economy by one of the two general systems, which pervade its entire extent; not, however, by that portion of each system which extends from the centre to the extremities ; but, on the contrarv, by that which returns from the surface to the central parts. The veins convey the foreign substance itself into the circulation, in proprid persond, if we may be allowed to use the expression ; while the nerves only transmit impres- sions of a peculiar nature. It is a well-known fact that the venous circulation is frequently encumbered with putrid substances small fragments of mortified tumours, fibrinous clots and so forth; while the nervous fibre exerts over our organs a subtle and penetrating influence, and merely by transmitting the shock it has received, produces modifications of the most extensive character. We have sufficiently proved, in the course of these Lectures, that the sensitive fibre alone enjoys this property; yet, in a