eases; only in the towns they appear and prove fatal at an earlier stage of life. We cannot, therefore, directly trace the specific influence of an impure atmosphere; we can only suppose it to accelerate the access of disease from other causes, or to render it more fatal. But the phenomena are essentially the same, whether they happen in great cities or in country villages; in neither the one nor the other of these situations do we meet with diseases that are absolutely peculiar, and exclusively confined to the spot on which they appear. We cannot, therefore, acknowledge distinct causes as generative of disease, in large cities, from which the country is wholly free. We can only suppose that in cities the causes, be they what they may, are more active and concentrated.

There are those who appear to think that the essential difference of climate consists merely in a difference of temperature. They propose, by artificial methods, to correct the evils which they attribute to the coldness of our atmosphere; and they hope, by what they call a regulated temperature, to arrest the progress of, and even to cure, the most frequent and most fatal of our diseases. But it should be considered that though temperature has very considerable influence over the symptoms of disease, it has little or none over its general results and final termination.

In different climates disease assumes different forms, and fixes its seat upon different organs. In the East Indies, practitioners hardly see the greater part of our European diseases; rheumatism, catarrh, pleurisy, peripneumony, headaches, and toothaches are wholly unknown. But instead of these almost universal European diseases, another class, which are hardly heard of with us, except perhaps for a month or two toward the close of the summer, are habitual and universal. They occupy the liver, intestines, and mesentery, occasioning redundancy of bile, hepatic congestion, fluxes, and other disorders indicative of increased mobility and irritability of all the parts of the system, comprehended within the extent of the cœliacal and portal circle. These differences may, probably, be justly ascribed to permanent differences of temperature, though we are wholly ignorant of the mode in which they operate. But in point of general salubrity, the warm climates do not appear to have any advantage over the temperate; and, therefore, though the symptoms of some particular cases of disease may be alleviated by the mere avoiding of cold, yet it is highly improbable that such a precaution alone can avert or much retard the fatality of any fixed diseases.

To the proposal for the use of a regulated temperature in consumption or other diseases, there lies a fundamental objection, independent of the weakness of the proofs by which it is supported; this is, that it is applicable only to persons in easy circumstances. If there is any law in the government of the universe more steady than another, it is that nothing, which is truly useful, is not useful to all. Neither food, nor clothing, nor medicines, nor a covering from the atmosphere, nor knowledge sufficient for the guidance of life, are confined to any rank of society. Every plan of acquiring, whether it be health or happiness, which is not communicable to all, will assuredly prove abortive.

Though temperature alone will not counteract powerful morbific causes, whether of diet or of locality, it cannot be doubted, I think, that warmth is, within certain limits, favorable to the human constitution. But a change of climate includes commonly a great change of other circumstances besides temperature, and it illustrates most forcibly the effects of locality. These effects, though men have very indistinct notions as to their immediate causes, are universally acknowledged and acted upon. Upon it is founded the advice given in most obstinate diseases, to try what is called change of air. When we reflect upon the astonishing difference in the salubrity of different places, we see clearly upon what foundation this advice rests; and can feel no surprise at the great benefit which has been often experienced in obstinate diseases from a change of residence. Complaints, which have resisted the most judicious treatment, often quickly subside, as it were spontaneously, by quitting the situations in which they were formed. How many gain health instantly by going out of London? This is a point on which the voice of all ages has been unanimous. "In young persons afflicted with epilepsy," says Hippocrates, "changes effect the solution of the disease, principally of age, and place, and manner of life." The daily experience of every individual corroborates, in some degree, these remarks. There hardly exists a person of some experience in life who has not found, with a change of residence, some corresponding change either in feelings or health.

Upon these principles, if a person is suffering under an habitual disease, which resists medical treatment and threatens to shorten life, a more reasonable proposal could not be made than for him to remove to a situation where the bulk of the inhabitants had been observed to enjoy the best health, and to attain the greatest longevity. The ancients, as we are informed.

by Vitruvius, inspected the livers of the animals of a country in order to judge of the salubrity of its soil and productions. They did not act without reason. But our authentic registers of mortality afford a still surer guide; and I can hardly avoid wishing that they had been more frequently consulted for this purpose. Such a measure would surely be more rational than sending the sick all promiscuously to the sea, or, as Dr. Gregory has somewhere said, from one foolish watering place to another foolish watering place. In these things, however, fashion has been more powerful than principle; and so it may be expected to continue.

It is obvious, from many considerations, that the quantity of mortality is quite inconsiderable when compared to the general quantity of sickness; though this is a subject on which it is impossible to form a calculation. Men are not always shortlived because they are unhealthy, nor is great and apparently very dangerous illness, in different stages of life, incompatible with arriving finally at old age.* Little dependence, therefore, can be placed upon solitary observations with regard to the effect of particular habits, or modes of treatment. Few are duly qualified to form a just estimate of such things. I am apt to think that, in this respect, even the sage Cornaro deceived himself. It becomes then of the first consequence to view mankind as much as possible in the mass, and to obtain, as far as it is in our power, general results.

If, in fact, it is established by such observations that our diseases are the offspring of our habits, and of the circumstances in which we are placed, it must follow that of those who are placed in the same circumstances, however various are the forms and external appearances of disease, there must be an absolute identity in its essence. This must, I think, be correctly true of all those diseases which arise, as it were, spontaneously in the habit, independently of accidental circumstances. Nor can I exclude from this class the acute inflammations which are commonly regarded as a species of accident, produced by some foreign circumstance recently applied, as severe cold. The inflammations require a peculiar state of the constitution for

A remarkable example of this may be found in the Commentaries of the elder Heberden. 66 That very eminent physician, Sir Edward Wilmot, before he had completed his twentieth year, labored so severely under a consumptive disorder, that, as he himself told me, not only his relations but the most skillful physicians despaired of his recovery; he lived, notwithstanding, and enjoyed good health beyond his ninetieth year."-Heberden Commentarii, p. 324.

their production, as well as an immediate external cause; and they have their seat in various organs, according to the different time of life in which they occur. It is highly probable that when the acute inflammations prove fatal, the vitality of the system is destroyed, as it were, before the attack. Šuch persons should be considered, therefore, to be as completely worn out as if they had died of a lingering disease: of dropsy, or of consumption.

In a system like that of the human body, consisting of a congeries of different organs, each independent, and endued with peculiar powers and actions, but each likewise connected with the whole, and conspiring to a common end, there can be no difficulty in comprehending how the same agents should, upon different individuals, produce dissimilar effects. Nature, or the supreme wisdom which has formed, sustains, and animates the universe, seems to delight, if we may venture so to speak, in conjoining the most admirable simplicity with the most astonishing variety. From a few elements, and which our ignorance probably makes more numerous than they are in fact, we see living beings, whether vegetables or animals, so diversified that human life is too short to permit us to become acquainted with their various forms and properties. Is it then improbable that a few agents should produce various effects upon the bodies of men—a race of beings no two of whom are alike, and of whom not one individual preserves an absolute identity for two successive days, or even for two successive moments? A familiar example may render this truth more evident. How variously does wine affect different individuals? One can bear two or three bottles, another is giddy with half a glass-full; one becomes jocund, another splenetic; one wakeful and sprightly, another heavy and sleepy; one good-humored, another is driven to madness. What we see in the effects of wine, we can readily suppose of other agents.

If this were a simple matter of speculation it would be of little moment. But I have dwelt upon it on account of the practical inferences to which it obviously tends. If we can show that the antecedent causes of various diseases are the same, though the immediate symptoms may demand various remedies, yet the radical treatment may and ought to be the same, however opposite the apparent forms of the disease may be. This evidently is to remove the antecedent causes as much as it is possible. Then, if the radical and inherent powers of the system have not been destroyed, it may be expected, if not wholly to recover, at least to show a constant tendency to

recovery. In what degree this can take place it is in vain to speculate, independent of experiment. Each case will have something distinct and peculiar. The bow which has been long bent will, when the string is cut, tend to regain its straightness; but it may ever retain some marks of the force impressed upon it. Suppose this bow to be the branch of a living tree, the result may be still the same; but the cases will be more parallel.

When we say that the phenomena resulting from the action of the same causes must be deemed to be essentially identical, we must limit ourselves to the strict terms of the proposition, and by no means conclude that no morbid appearance can arise in the body which may not be distinctly traced to such causes. It must be considered that an animal body is a machine endued with internal and inherent self-moving powers, which it preserves, and which are in action as long as life continues. Changes take place from the operation of these inherent powers, which, if they are attended with pain, and a derangement of the ordinary functions, are considered as diseases. The teething of children is an instance of this. In like manner acute diseases may frequently be suspected to be natural processes, taking place, perhaps, in morbid bodies. In the present state of our knowledge, and the great obscurity in which these subjects are involved, as it would be the height of presumption to affect to explain all the phenomena of life, so would it be captious and uncandid to object every accidental and unforeseen occurrence. We must content ourselves with approximating to what appears, upon the whole, to be the truth. Anomalies and difficulties must be expected to arise which, perhaps, we may never be able to elucidate; and the explication of which must be left to time and the industry of future inquirers.

These few remarks, which appear naturally to follow from the facts established with regard to the laws of human mortality, may be sufficient to render probable the general principle, that the efficient causes of constitutional diseases and premature death are to be sought for in the action of the substances which are applied to and affect the body. But to gain useful information we must enter into a more particular examination of what these really are.

Now any substance whatever which produces a change either in the composition, in the sensations, or in the motions of the body; in a word, which affects it as a living system, may be justly called an agent, and as such must conspire toward the general result either of healthy or diseased action. As such,