Of the Relation between the Phenomena of Fever; or the Theory of the Disease.

In the preceding chapters it has been shown what are the real events which take place in fever, the assemblage of which constitutes the disease: it has also been shown in what order these events succeed each other, and upon what conditions of what organs they depend. To assign further the true relation between these events, is to establish the theory of fever in the only philosophical sense of the term theory: and that relation must already have suggested itself to the mind of the attentive reader.

We have seen that the first indications of disease are clearly traceable to the nervous system: that the disorder of the functions of the brain and spinal cord with which the attack always commences, demonstrates that these organs form the primary seats of the malady: that the derangement in the functions of these organs is truly invariable, and is invariably the first morbid condition that is observed to take place: that there never was a case of fever, from the slightest to the most severe, in which these organs were not in a greater or less degree in a disordered state, and in which that disordered state did not precede every other. This affection of the nervous system then, the invariable antecedent of all that follows, is the primary essential event in the morbid series which constitutes fever.

What the real nature of this primary affection of the nervous system is, we are wholly ignorant, and we ought at once to confess our ignorance. We have already entered into some considerations, derived from the difference in the order in which the phenomena of fever and of inflammation succeed each other, to show that these two diseases are not identical.^[30] When these phenomena are still more attentively considered, other differences are observable between them, which confirm the opinion that the two diseases are not the same. Not only is derangement in the nervous and the sensorial functions invariably the first in the series of morbid events in fever, while it is not the first in inflammation, but that derangement is always much greater in the former than in the latter, and proceeds in a regular and determinate course, such as has been fully explained in the preceding pages, and to which there is nothing analogous in the progress of inflammation.

To the condition of inflammation a peculiar but an unknown condition of the blood-vessels appears to be indispensable. To the state of fever, no such condition of any part of the vascular system, as far as we have the means of judging, is absolutely indispensable, although it be very commonly coincident. No such condition appears to be present, at least no such condition has yet been ascertained to be present, either in the very mildest or in the severest form of the disease: at the latter extreme of the scale, at least, we might expect to find the most striking and unequivocal indications of the existence and operation of inflammation, were that agent really present; and yet it is precisely here that the ordinary signs of inflammatory action are completely absent.

Moreover, we have no example of instantaneous death by the sudden excitement of inflammation in any organ, or in any number of organs: inflammation is a process: a certain number of events take place in a certain order; and there is always, as far as has been hitherto observed, some interval between these events. A case is recorded in which inflammation of the bowels (acute enteritis) proved fatal, as was supposed, in eight hours from the commencement of the attack; but so rapid was the process, that the intelligent surgeons who witnessed it doubted whether the time when the disease began could have been noted accurately: at all events, it does not accord with the best-established facts relative to the process of inflammation, that it should prove fatal without the lapse of some hours. Fever, on the contrary, does not need as much as a single hour to complete the work of death. It is well known that the poison which, in a certain state of concentration, produces fever with the ordinary period of duration, in a higher state of concentration produces instantaneous death; and that, in certain climates and seasons, it is not uncommon for persons previously in sound and vigorous health, on exposure to that poison, to sicken and to die in a shorter space of time than is requisite, under ordinary circumstances, for the mere formation of the inflammatory process. The state of the system, in the primary attack of fever, and the state of the system in inflammation, do not, therefore, appear to be identical. The truth is, that we do not know what the real state of the system is in either case, but we see that the phenomena of the one differ from those of the other; to conclude, therefore, that the states are the same is not a sound induction. While, then, we are constrained to admit that we know nothing of the nature of the primary affection of the nervous system in fever, the closest consideration of all the phenomena alike constrains us to conclude, that that affection is peculiar and specific.

This peculiar and specific affection appears to be much more analogous to the condition into which the nervous system is brought by the application of certain poisons, than to that which is proper to pure inflammation. The more closely and extensively the subject is investigated, the more clear and satisfactory the evidence becomes, that the great primary cause of fever is a poison, the operation of which, like that of some other poisons, the nature of which is better understood, and the action of which has been more completely examined, is ascertained to be upon the nervous system. How these poisons act upon the nervous system we do not know, nor can we possibly know, as long as we remain so profoundly ignorant of the nature of the action of the nervous system in the state of health.

It may be considered then as established, that the primary morbid condition of the body, in fever, consists of an affection of the nervous system, which there is reason to believe is of a peculiar and specific nature, although that nature be at present wholly unknown.

This specific derangement of the nervous system having continued for some time, the vascular system becomes disturbed. How the nervous system so influences the vascular as to bring it into the morbid condition into which it passes, is as unknown to us as the peculiar affection of the nervous system itself. That there is the most close and intimate connexion between these two systems, and that they exert over each other the most important influence both in the state of health and of disease, are in the present state of our knowledge ultimate facts.

With two apparent exceptions, (whether these two cases form real exceptions may still admit of doubt) the vascular derangement connected with, and dependant upon nervous derangement, passes sooner or later into true inflammation. Of this we have the most complete and indubitable evidence—evidence derived both from changes, the known results of inflammatory action, produced in the structure of organs; and from the generation of new products, such as are formed by no other known process but that of inflammation. Almost every change of organic structure which inflammation is ascertained to be capable of producing, is found to take place in fever: almost every product which inflammation is ascertained to be capable of forming, is observed to be generated in fever: it is not possible to doubt, therefore, that the morbid condition into which the vascular system is brought in the progress of fever, is that of inflammation. In what circle of organs inflammation is peculiarly liable to be excited in this disease, by what particular character febrile inflammation is distinguished, and what remarkable differences it exhibits in intensity and extent, have been fully illustrated.

It follows, then, that the second event that takes place in the morbid series constituting fever, is inflammation.

But however really and constantly inflammation may take place in fever, and in whatever intensity, and to whatever extent it may be carried, yet the inflammation is never pure or simple: the condition of the inflamed organs is never the same as that into which they are brought by mere phlegmasia: there is always inflammation, and something else: and if what we have so much insisted on be true, this must necessarily be the case, because the state of inflammation succeeds to another, a distinct, and a pre-existing condition of the system: that something else is the unknown, but the peculiar and specific affection of the nervous system, which has already been stated to be the invariable antecedent of whatever subsequent affection may take place. Thus this affection of the nervous system is not only the invariable antecedent of every other condition, but it is omni-present with every other condition, and its presence is a most powerfully influential presence; it operates at every instant, in every organ, and every function of the economy, although, as we have seen, its operation is peculiarly great, and, as far as we can perceive, specific in certain organs and functions. The combination of this nervous affection with inflammation, and the influence which this combination exerts over the inflammatory state, we express by saying that the inflammatory state in fever is modified: we see that inflammation is present, but we see that it is not the same as inflammation in a pure phlegmasia: we see, as has just been stated, that there is inflammation, and something else superadded; namely, a peculiar affection of the nervous system, which gives to the febrile inflammation a peculiar character, or which modifies it in a specific manner.

It has been stated that there appear to be two exceptions to the universality of the presence of inflammation. Of these exceptions, one is exemplified in the mildest form of the disease. In every case of fever, the function of the vascular system is disturbed in a greater or less degree, as has been fully shown: but the doubt is whether that disturbance invariably pass into the state of inflammation. Since the morbid condition of the nervous system, in the mildest case, remains only for a certain period, and then uniformly gives place to the return of health, there seems to be no possible means of determining this question. And even in the second case, where the intensity of the nervous affection is incompatible with life, and death follows with extreme rapidity, the real condition of the vascular system appears to be equally doubtful. In both, that condition may possibly be a modification of one and the same state, and that state may be identical with inflammation—inflammation existing in different degrees of intensity. On the other hand, both may differ essentially from the state of inflammation. The nervous affection in the first may be too slight to excite inflammatory action, while in the second it may be so overwhelming as completely to oppress every function of the economy, and therefore, instead of exciting, may paralyse the capillary blood-vessels; and consequently paralysis of the capillary vessels, instead of intense excitement of them, may possibly be the real condition of the vascular system, for example, in congestive fever.

But however this may be, the only difficulty in the subject relates to these two forms of the disease—the very mildest and the very severest. In all the intermediate cases, the condition of the vascular system is clear and certain. In all these, there can be no more doubt that that system is in a state of true inflammation, than there can be that the capillary vessels of the pleura are in a state of inflammation in pleuritis. Yet, as we have just stated, in fever the inflammation is never the same as it is in pleuritis. In fever there is a combination of a specific affection of the nervous system, with that specific affection of the vascular system, which constitutes the state of inflammation: in pleuritis there is the specific affection of the vascular system, without the specific affection of the nervous; and this combination of the two affections in fever modifies the nature of febrile inflammation.

This view of the constitution of fever appears to explain in the most luminous and complete manner every peculiarity of the febrile state: to reconcile all its apparent anomalies, with which few who have studied the subject have not been perplexed: to establish the true distinction between fever and inflammation; and to show why the phenomena exhibited by these two affections are so essentially different, and why therefore each requires a different mode of treatment. In this point of view no theory was ever more eminently practical, or led to a more guarded practice. Inflammation does not lose its nature by being combined with that peculiar affection of the nervous system which converts it into fever; it only modifies its state: the remedies proper for fever do not differ from those which are effectual in inflammation; they only require to be modified in accordance with the modified nature of the disease. He who believes fever to consist of an affection of the nervous system alone, every other affection that may be combined with it being accidental, will rarely think of using the lancet: he who believes fever to consist of inflammation alone, and overlooks the presence of the nervous affection, will be apt to carry the employment of the lancet too far: he alone who embraces the view of both, brings within his own all the phenomena: he alone adopts a sound theory of the disease, and we now see that he alone is likely to be led to a sound practice. When the theory of a disease collects, arranges and points out the true relation between all its phenomena, there is good reason to conclude that that theory is sound; but when it moreover directly leads to that treatment of the malady which experience shows to be the most safe and the most effectual, its truth is established by every test that can be applied to it.

The consideration of the diseased states of the other systems and functions that take place in fever, need not detain us long. The respiratory appears to be the next function that becomes deranged. The intimate and inseparable connexion which physiology teaches us subsists between the respiratory and the circulating systems, might lead us to anticipate the fact which pathology demonstrates. We know that the respiratory system is constructed for the circulating: that the form, the extent, the complication of the respiratory apparatus depend entirely upon the quantity of blood that is to be regenerated, and the degree of perfection with which that regeneration is to be accomplished. It is therefore impossible that any considerable derangement in the function of one of these systems should continue long, without being accompanied with a proportionate derangement in the other. The function of respiration cannot be materially deranged, without producing a morbid condition of the blood, that vital fluid which it is the specific object of the process to purify and regenerate. The function of secretion depends upon the quality of the blood conveyed to the secreting organ, upon the action of the capillary vessels of that organ, and upon the supply of nervous influence received by those vessels; it follows, that in a disordered state of the nervous, the circulating and the respiratory organs must be attended with a derangement in the process of secretion; while the excreting being necessarily connected with the secreting processes, the vitiation of the one cannot fail to occasion a corresponding deterioration of the other.

Thus we see that the organs and functions deranged in fever are closely and inseparably connected: that no continued disorder can take place in the one, without producing a proportionate disorder in all the others: that a peculiar and specific affection of the first, according to the established laws of the vital economy, invariably produces a peculiar and specific affection of the second, and the second, a third, and so on throughout the circle. And now we see why a certain number of organs are invariably affected in fever; why these organs invariably become affected in a certain order; why the nature of their affection is invariably the same; and why, finally, the ultimate condition of the system, the general result of these individual morbid changes, never varies.

Writers on fever in general have confined their account of the phenomena of this disease to an explanation of the relation between the cold and the hot fits. Were their success in establishing that relation as complete as it is defective, they would still have done little or nothing, by a view so incomprehensive, towards establishing the theory of fever. Both the cold and the hot fits, about the exposition of which such a theory is alone concerned, are themselves accidents, since in the most formidable and dangerous forms of fever, the supposed relation between these phenomena is not only constantly disturbed, but often the phenomena themselves do not occur, it being one of the very characters of some of the intensest fevers, that the temperature is little changed, and that the diminished temperature which may be, or which may have been present, is never succeeded by any increase of heat. The true theory of this, as of every other disease, must be sought in the study of its pathology, and can be found only by comparing the pathology of the organs ascertained to be affected with their physiology. The cold stage of fever, when it exists, is produced by a disturbance of the functions of the circulation and of the respiration, and these functions are disturbed, because the organs in which they have their seat no longer receive their accustomed and their requisite supply of nervous influence from the nervous system. The hot stage, when it exists, arises from a disturbance of the same functions: and the reason why we cannot assign with precision why the same cause produces in the one case a diminished, and in the other an increased temperature, or why the temperature is disturbed at all, is because we do not know with precision on what circumstances in the animal economy the generation of heat depends: when the physiologist has clearly and completely ascertained all the circumstances upon which this process depends, the pathologist will probably have but little difficulty in tracing with equal clearness and completeness the connexion between the disturbance of that process, and the commencement of the febrile state.

In conclusion, then, the doctrine of fever which appears to approximate most nearly to the truth, may be summed up in few words. The immediate cause of fever is a poison, which operates primarily and specifically upon the brain and the spinal cord. The diseased state into which these organs are brought by the operation of this poison, deprives them of the power of communicating to the system that supply of stimulus (nervous and sensorial influence) which is requisite to maintain the functions of the economy in the state of health. The organs, the seats of the functions, deprived of their supply of nervous influence, become deranged, the derangement in each taking place in a fixed order, and in a determinate manner. Subsequently to the nervous and the sensorial, the organs the next to suffer are those of the circulation; then those of respiration; and, ultimately, those which belong to secretion and excretion. The condition of the nervous system which produces this derangement in this circle of organs, occasions further, in that portion of the circulating system which consists of the capillary blood-vessels, that peculiar state which constitutes inflammation: hence inflammation is almost always established in one or more of the organs comprehended in the febrile circle, and sometimes in all of them. The peculiar and primary affection of the nervous system, which is here assigned as the cause of inflammation, does not become identical with inflammation, but superadds the morbid condition of inflammation to its own; does not lapse into or terminate in the inflammatory state, but accompanies it, and by this combination modifies in a peculiar manner the inflammatory process.

The great practical conclusion to be deduced from this doctrine of fever is, that while the inflammatory processes that are thus set up in so many important organs, greatly aggravate the severity of the disease, and ought to be constantly kept in the view of the practitioner, both on account of their own peculiar danger, and also because they are perhaps the only real states over which he has any control, yet that these inflammatory processes do not alone constitute fever; that their removal, though essential to the cure, will not complete the cure; that another, a primary, and a most formidable disease, is at the same time to be contended with, and that the presence of this distinct and primary disease requires very important modifications in the treatment of the inflammatory condition.