painful and difficult effort in recalling the entire consciousness of the waking state.

Among the causes which influence sleep and dreaming, I doubt whether changes in the state of the atmosphere have been sufficiently noticed. My attention having been casually drawn to this point some years ago, I have since made many observations upon it; and with more uniformity of result than could be expected, seeing the many other causes which act concurrently; as time, quantity and kind of food, excitement or fatigue of mind or body, habit as to times of sleep, and the variations due to actual disease. Removing these ambiguities as far as possible, I have found that any very sudden and considerable fall of the barometer produces in many persons a sort of lassitude and drowsiness, followed by restless and uneasy sleep, or frequently a state of laborious dreaming. It be doubted whether this influence depends on changes in the balance of circulation thus produced, or on alterations in the electrical state of the air concurring with its change of weight, and affecting (as we have often cause to suppose likely) certain functions of the nervous system. However this be, I cannot doubt the reality of the fact as one of frequent It is indeed merely an example, among so many others, of the partial subjection of the phenomena of life to the agents which are ever in movement around us.

may

Occurrence.

* During the month preceding the time when I am now writing (April, 1836), there have been two or three very singular and sudden depressions of the barometer (one of more than an inch within a few hours, from a point already low), attended by gales of unwonted violence on the southern and western coasts of England. It has occurred to me on all these occasions, but particularly on the latter, to observe similar influence, as respects sleep, on myself and many different persons; taking for evidence those in ordinary health, rather than such as were suffering under malady at the time.

456

CHAP. XXVII.

ON THE INFLUENCE OF WEATHER IN RELATION TO DISEASE.

AMIDST all the opinions and phrases current on this subject, it is singular how little real knowledge has been gained, or applied to practice. The difficulties of the inquiry are great, both from the complexity of the agents concerned, and from that of the organs and functions acted upon. Yet with the certainty we have of the extent, variety, and unceasing nature of this influence, it is manifestly a field of research, where patient observations and averages cannot fail of affording the most valuable results.'

On this topic, as on many others in this volume, the remarks which follow do not profess more than to give a certain degree of method to its several parts; and to suggest the conclusions, chiefly practical in kind, which appear to have engaged least attention. Some of the points, only touched upon, or briefly treated, might well furnish material for separate volumes, from their importance, and the scope they give to experimental research.

The subject, taken in its whole extent, admits of being distributed into several separate objects of inquiry.

The history of the diseases of particular climates, though still deficient in many respects, and altogether wanting for

*Nor is attention to this subject always solicited by the sick themselves. Besides the accustomed looseness of inference on every point regarding health, it is singular how averse many patients are to attribute any effects to the influence in question. Every other cause is invoked rather than this very powerful one.

many important localities of the globe, is perhaps that part which has hitherto been most successfully cultivated. For this object, however, observation is not to be limited to the effects of different meteorological states on the animal economy. It of necessity extends to many other local conditions, not fitly coming under this head, yet blending with and modifying all those which depend on climate alone; and requiring to be specified before inferences can rightly be drawn from the latter.*

The same may be said of that part of the subject which respects the climate of particular places, and their relative fitness as residence for invalids. Research here has been chiefly confined to the case of those labouring under pulmonary disease; and the observations with this view directed to averages of temperature, comparative quantity of rain, and prevalence of particular winds. Even, however, where it has been possible to attest these facts by averages of sufficient length, the difficulty remains of comparing other local circumstances, less obvious indeed; but which modify, and are often more than equivalent to, the direct effects of climate. And it must be added further, that this is a subject on which fashion, hasty observation, and mistaken methods of inference in the world at large, have very great influence. Accordingly we find that our actual knowledge, though extended and better assured by two or three valuable works, is still wanting in

The want of exactitude in noting these local conditions, which I have often had occasion myself to observe, has been most judiciously commented upon by Dr. James Johnson, in his work on the Diseases of Tropical Climates. Inferences, for example, can never be useful or admissible, which apply to the vast regions and various surface of India, as if it were one locality and a single climate. This is a strongly marked instance; but the comment applies to many others, where medical description partakes of that vagueness and want of attention to specialities, which belongs to all popular opinions on the subject.

certainty; and the practice founded upon it often singularly vague and of doubtful benefit.* The truth of the avowal will be admitted by every physician, who candidly looks to this part of the treatment of disease.

Another view of the subject, less exclusive than either of the preceding, is that of the relation of the several states and changes of atmosphere to the various functions of the body; a wide topic, abounding in curious results, and these of equal interest to physiology and pathology. Those which especially concern the former, though more or less at all times matter of popular observation, have only of late been taken into the domain of science. The researches of Dr. W. F. Edwards and others, while adding greatly to our knowledge both in extent and exactness, show how much is yet to be learnt, before we can appreciate the influence even of the most familiar agents around us. Every part of the history of disease affords the same inference. We feel these agents to be in perpetual operation; some of their more obvious effects in producing disease are currently understood by all; medical knowledge has registered a few others, in which certain disorders are manifestly produced, or rendered epidemic, by particular states of weather; - but there still remains behind much more than has yet been acquired. Scarcely is there a single branch of science which in its progress may not be brought to contribute to this object. And without claiming any present certainty for the connexion which some physiologists affirm between electrical and nervous agency, it must be allowed that this part of science, in particular, is likely to explain hereafter some of the more singular effects of the atmosphere on the human body.

I may name as the best work we have on Climate, that by Sir James Clark; very valuable in local details, and in the practical inferences founded upon them.

The foregoing observations apply to the several modes under which this subject may be viewed; each having its peculiar objects, while all serve for mutual illustration. The remarks which follow, have reference especially to the influence of certain states of air or weather in producing morbid conditions of the body; either in their immediate effect, or indirectly by evolving or giving greater activity to other causes. The latter distinction must be kept in view, as far as our knowledge will allow; since, doubtless, many of the diseases of season and climate are derived from such secondary causes, rather than from those more obvious to common remark.

With this exception (under which we must include the exanthematous and certain other fevers) the prevailing diseases of each season, as a class, are to be referred chiefly to the continuance, or more frequent repetition, of the causes by which particular cases of these diseases are produced. I need not, from their familiarity, enumerate those which are usually cited, though not perhaps with much precision, as severally predominant at different seasons of the year. Taking them collectively, they furnish certain average results of mortality, which form a very interesting and important branch of medical statistics, and have been greatly extended of late years in number and exactness; promising for the future various conclusions of more general application than any we now possess.

On this subject more is often to be learnt by carefully and continuously noticing the phenomena of one locality, than by diffusing the research over many. Each mode of inquiry has its value, separately and for mutual illustration; but that perhaps is most instructive, which connects the prevalence, type, and change of disease on a single spot, with corresponding conditions in the atmosphere around it. Observations of