The different states of the body in the cir cumstances just referred to deserve special attention, because they are reproduced in others, where the cause not being apparent they seem to be spontaneous, though they are in fact, as we shall have occasion to see, under the influence of an analogous cause. We sup pose that on the first exposure to cold during rest, the reaction from the afflux of blood to the capillaries is slight, and that the cold is even sufficiently intense to produce an opposite effect, that is, paleness of the part chilled. To this symptom of the action of cold, shiver ing is superadded in various degrees of inten sity. If recourse be now had to exercise, this state will last for a period long in proportion to its intensity, until violent and prolonged mo tion have restored the temperature. If the exercise be continued, the heat increases, and even rises above its degree at starting ; in this case it first restores the proper heat of the skin, and then causes this tegument to assume a red colour, which may become extremely intense. To this second state succeeds a third, in which the skin, which had hitherto been dry and un perspiring, becomes soft and finally bedewed with moisture. Here, then, we have three different states induced under the influence of cold acting at first without opposition on the part of the system, and then combated by powerful and voluntary reaction. First, we have coldness, paleness,and shivering; secondly, heat and redness; thirdly, moisture of the skin and sweating. In making the application here of what has been said above upon the repetition of these acts, we perceive that at the same degree of external temperature the effects which at first, and under other circumstances, would follow the impression of such a degree of cold, may cease to be felt. This happens from the constitution having improved under the actions and their effects, which have been detailed, and that it is in a state, with the assistance of its own inherent powers of insen sible and involuntary reaction, to resist refrige ration. But do we not, when we strengthen the constitution to such a pitch as enables it to resist an influence which was a cause of incon venience to it previously, cure it of an infir mity ? It is obvious from what precedes that the temperature of the body may be indiffe rently affected, either by a great fall in that of the air, or by an insufficient production of heat. The temperature of the body tends to sink equally when, producing a great deal of heat, it is exposed to severe cold, or when, producing little heat, it is exposed to a moderate warmth. In either case the effects upon the economy will be analogous without being identical. I n each case there will be a keen sense of cold according to the depression of the external temperature on the one hand, or the slightness of the evolution of heat on the other. In the latter case the insensible reaction will be ex tremely limited, as well as the voluntary reac tion, on account of the deficient energy. But there are still resources within the economy. It is then that the involuntary and violent reaction of which we have already spoken takes place. The circulation and the respiration increase in rapidity spontaneously. In the case which we have just supposed, there will be certain series of phenomena, analogous to those we have described as occurring in the instance of a strong individual exposed to the influence of severe cold, who suffers from it at first, and subsequently opposes and vanquishes it by means of a violent and voluntarily superinduced reaction. When the faculty of engendering heat sinks to a certain term, there will be not only a vivid sensation of cold even in summer, but all the other consequences of exposure to a low temperature, such as paleness, shivering, &c.; by-and-by the involuntary reaction will not fail to take place; the respiration and circulation are accelerated, and end by restoring the temperature, if the lesion of the calorific power have not been too extensive, the skin being first hot and dry, and subsequently hot and moist. IIere, consequently, we have the three periods precisely as in the case previously described : 1st, coldness, pallor, and shivering ; 2d, acceleration of respiration and circula tion, accompanied in the second period by dry heat, and in the third by sweating. There is therefore the strongest analogy in the two cases. They resemble one another in the cha racter of the phenomena, and the order of their succession. This is so obvious as merely to require mention ; there can be no occasion for more particular illustration. They have also the strictest relationship in their causes, without these, however, being identical. In the first case the individual produces a great deal of heat, but he cannot engender enough by the ordinary and insensible reaction, in conse quence of which he has recourse to the violent and voluntary reaction, which soon produces the desired effect. In the second, the indivi dual produces little heat, and the economy may suffer from this diminution of the calorific faculty to the extent of finding itself incapable of restoring a sufficient degree of heat by means of a violent and voluntary reaction. The violent and involuntary reaction then succeeds, and pro duces all the effects of that which is put into play under the empire of the will. Nor is the resemblance limited to immediate results. It further extends to the remote and definitive effect. For in either case the violent effort ceases after a certain interval of variable extent, according to various circumstances ; and a state of tranquillity conies on in which the body has recovered the faculty of engendering by the ordinary means the quantity of heat ne cessary to the comfortable existence of the in dividual. After this the repetition with greater or less frequency of the same acts ends by restoring the calorific function to the state in which insensible reaction suffices to maintain it in its sufficiency. In the first ease it is a strong individual able to make the voluntary and energetic efforts required to remedy the inconvenience he suffers. In the other instance it is an individual who has not the strength requisite to make such efforts. In this case nature supplies the deficiency by exciting directly the motions of circulation and respira tion by the painful impression of cold. Al though the condition of the first be the state of health, and that of the second properly a morbid state, they nevertheless hare many relations in common, which differ princi pally in degree. Does not the robust indivi dual experience an inconvenience for which he finds a remedy in violent and repeated efforts? however robust he may be under ordinary cir cumstances, in the extraordinary condition in which he is placed the usual vital processes no longer suffice him. Ile must have recourse to violent means which disturb the economy ; and by a repetition of the same efforts at diffe rent periods, that is to say, in fits or paroxysms, he ends by so far fortifying himelf as to be able to do without them. Is not this tantamount to remedying a relative infirmity of constitution ? Let its degree increase but a little, and the infirmity becomes disease. This parallel is not founded on vague and superficial resemblances, but on determinate and fundamental relations. There is not one essential point in the compari son which does not rest on the result of direct experiments, most of which have been quoted in preceding parts of this article. What must be done to justify the similitude of these two states ? With regard to the state of health the connexion of phenomena having reference to the hygienic and voluntary reaction is well known. W'ith reference to the relation between the symptoms in the morbid state and the morbid reaction, it remains to be proved that under circumstances where there is but slight production of heat, the feeling of cold may induce acceleration in the respiratory and circu latory motions. Now ithas been established by experiments already quoted, that there is reac tion of this precise kind in such circumstances. We have seen, for instance, that when a bird, naked or scantily covered with feathers, is taken from the nest and exposed to the air even in summer, it speedily begins to shiver, and to exhibit a reaction in accelerated motions of respiration, which is followed by, and indeed implies increased rapidity in the motions of the heart and current of the blood. it were also proper to show that the cold state may, by means of the violent and involuntary reaction, induce the restoration of heat. This is also susceptible of proof by means of direct expe riment. To this end an individual (a young bird from the nest) must be chosen of such an age that the temperature will not be apt to fall ton low on exposure to the air. If the
choice have been fortunate, it will be found that the temperature sinks in the first instance, and then rises, so that it may even surpass the de gree it showed at first, under the influence of the reaction occasioned by the acceleration of the motions of respiration and circulation. The proof here is, therefore, extremely satis factory. A creature in a state of health is taken and placed in circumstances in which the same essential symptoms are produced in the same order as in the morbid state which we have described. It can scarcely be necessary to say that the morbid state which we have described in man is that of simple intermittent fever. Not only in the beginning of this disease is there a feeling of cold, but recent accurate ob servations have shown, by means of the ther mometer, that there is actual refrigeration. There is, therefore, lesion of the calorific func tion in the sense previously indicated, that is, there is decrease in the power to produce heat. Subsequently the temperature rises whilst there is still more or less of the sensation of cold remaining ; but this only happens by vir tue of a general disposition of the nervous system. The same thing, in fact, occurs in a state of perfect health ; when the body has for some time been exposed to severe cold, the sensation continues for a certain interval after it has been restored to the normal temperature. It is of little consequence, as regards the sub ject which engages our attention, that there are some intermittent fevers which do not exhibit the phenomena of temperature that have been described. We are only interested in proving that some do occur which present them all,—a fact that has been demonstrated by the best authorities.
There is consequently in these cases a lesion of the calorific function, a lesion of which the essence consists in a diminution of time faculty of producing heat. In a constitution capable of re-acting by the acceleration of the respiration and circulation, we may observe upon this occa sion two principal modifications of the morbid state, which both depend on the same cause, but which differ in degree. The first is that described in which the reaction suffices to restore the calorific power to the degree com patible with health after one or more fits or paroxysms. With regard to the second, the diminution of the function of calorification may be so great, that the reaction may prove in adequate to restore it, not only permanently but even momentarily. There are in fact diseases of this kind ; there are many regular intermittent fevers that have no tendency to spontaneous cure ; there is also one particular form of the disease which proves speedily fatal without the intervention of art. This is that form of intermittent which is known at Home especially under the name of thefildire or cold fever. It often happens that the patient, unless suitably treated, dies in the cold stage of the second or third paroxysm ; sometimes he will even perish in the first.
It is easy to produce at will the essential symptoms of these affections even in their most formidable shapes, in animals in a state of health. All the young birds, for example, belonging to the group of those which at their birth have the weaker calorific powers, can be made to exhibit the phenomena in question. If, at the period of their exclusion or shortly after this, they be taken out of the nest, we have seen that they lose heat rapidly even in the summer season; and we perceive that any reaction of which they are capable by the acceleration of their respiratory and circulatory motions avails them nothing ; their tempera ture sinks in spite of this, till all reaction ceases by the increasing and now benumbing influence of the cold, so that they speedily perish. In these two extreme cases of dimin ished production of heat, there is similarity in the symptoms which ensue, with this difference, that in the algid intermittent there is lesion or a morbid state of the calorific faculty ; whilst in the other case the scanty production of heat is a normal condition in relation with the age of the subject. In the first, the constitution is seriously altered ; it must be restored or other wise the individual dies ; in the second, there is no alteration of any kind ; the individual only requires to be placed in circumstances favourable to the normal manifestation of the function to be restored. In the one the lesion is so great that there is no resource in nature abandoned to her own efforts ; art must interfere. In the other, nature provides against the scanty production of caloric in giving to parents the instinct to warm their young by the heat of their own bodies, &c.
We have seen that cold, when not of too great intensity, tended to strengthen the body by increasing the faculty of producing heat ; and farther, that with the progressive rise of the temperature in spring and summer the energy of this faculty diminished. This is what takes place with regard to those constitu tions that are in the most favourable relation with the climate. Let us now examine the nature of those constitutions that do not adapt themselves thoroughly to the changes of the seasons, and see what the consequences are with regard to them. Let us begin with the rela tion of these to the cold season of the year. It might be presumed a priori that those con stitutions that have a very limited capacity of engendering heat will not accommodate them selves well to the cold of winter. Their limited powers of producing heat will not ena ble them to repair the continually increasing loss of it arising from the depression of the external temperature. They consequently suffer in a greater or less degree from cold, perhaps not to any great extent in the first instance, as we shall have occasion to explain by-and by, but still in some measure ; and there are certain degrees of uneasiness and inconvenience that may be regarded as being still within the limits of health. There is even a certain, and that a pretty wide latitude in which the body may vary without trespassing on the line of disease. The uneasiness may only be ex perienced from time to time, and not even be always very manifestly referable to its proper cause. In other words the sensation may be something quite different from that ordinarily induced by cold; just as it sometimes happens that among weak constitutions the necessity of taking food is not always proclaimed by the feeling of hunger, but occasionally by some other distressing or painful sensation, with re gard to the true nature of which experience alone can enlighten us. In such a low state of the calorific power, the Faculty seems to lose strength still further, owing to the simple per sistence of the same degree of cold, and still more from the ulterior depression of the tem perature, in the manner we have seen when speaking of hybemating animals. This dimi nution in the temperature of the air sometimes occasions among weakly subjects morbid re action, the principal features of which have already been explained. From all that pre cedes, the constitutions that will be the most apt to suffer from exposure to cold will be those of the earliest times of life observed in man and the warm-blooded tribes generally, since it is at this epoch that they produce the least heat ; and as a corollary from this, we should infer that the mortality in early life ought to be greater during the winter season in this and other countries similarly circumstanced. It became a matter of peculiar interest to verify this inference from the experiments and reasonings of which we have just rendered an account. Messrs. Villertne and Milne Edwards accordingly undertook the necessary inquiries, entering upon extensive statistical researches with reference to the mortality of children in the different seasons of the year in France, and found that the mortality of infants from their birth to the age of three months was generally the greatest in those departments of which the winters were the most severe. For a similar reason, the natives of very warm climates who visit countries whose winters are excessively cold, run great risks of not being able to pro duce heat enough to compensate the loss they sustain from exposure to the low atmospheric changes, and thus of becoming obnoxious to disease and death in consequence. Those that have elasticity enough of constitution to meet this unwonted demand upon their calorific powers, experience an increase in the energy of the functions upon which the production of heat depends, by which they are brought into har mony with the climate. Others who are less robustly constituted complain loudly of the cold, languish, and finally perish if they do not find means of escaping from the destructive tendency of the cold.