Number of Deaths from Dysentery in each of the Four Quarters of the
following years.

must be remembered that when the number of deaths from
diarrhoea rose in the year 1849 to their maximum, viz. 3463,
dysentery was also more fatal than it had been for any of the
ten previous years; the deaths from this cause being 370,
whilst those from cholera were 14,125.

The Meteorological Conditions of the Air conducive to

Dysentery.

Humidity. The amount of wet weather during the whole of
this second constitution was remarkable, and undoubtedly
operated as a powerful cause in the production of the prevailing
diseases. When we reflect on the important part in the animal
economy that devolves on the cutaneous system, how necessary
the due performance of its duties is in order to preserve the
internal organs from being overtaxed, and how much its function
is influenced by external agents, we must consider the skin to
*Registrar-General's Third Annual Report, p. 354.

+ Op. cit. Fourth Annual Report, p. 335.
Op. cit. Fifth Annual Report, p. 472.

§ Op. cit. Eighth and Ninth Annual Report, p. 146.

|| Tables for 1853, for the fourteen years from 1840 to 1853.

be one of the grand media through which the atmosphere and its varied conditions act upon the viscera within. Twenty-eight miles of perspiratory tube are estimated to be distributed over an average-sized adult, seven million glands are constantly working to carry off redundant moisture and excrementitious matter; eleven grains, according to Seguin, are insensibly exhaled every minute, or about thirty-three ounces daily, which is nearly equal to the amount of the renal secretion, the latter being regulated by the former,-for in the warm dry air of summer the skin is stimulated to increased activity, and relieves the kidneys on the other hand, in the winter, exhalation from the surface is impeded by cold and moisture, and consequently the renal organs are called upon to supply the place of the skin. A simple illustration of the effect of a humid atmosphere upon the process of exhalation and evaporation is seen in the difference between the action of the dry and wet bulb thermometers which are used to test the hygrometric state of the atmosphere. In ascertaining the amount of moisture in the air, meteorologists have been for a long time in the habit of using several ingenious contrivances, but that most in use at present is an instrument having two thermometers attached to it; one of these has its bulb covered with thin muslin, to which is attached some floss-silk or cotton lamp-wick,-this is called the conducting thread, and is used to keep up a communication by capillary attraction between the water in a vessel placed below, and the layer of muslin on the bulb: the other, or dry thermometer, indicates the temperature of the atmosphere without reference to its moisture.

In the evaporation of water there is always a certain expenditure of heat, which is in the direct ratio of the amount of evaporation for instance, supposing that the air be so saturated with moisture as to suspend evaporation from the wet bulb thermometer, no extra heat being expended in the conversion of water into vapour, the two thermometers would indicate the same degree of temperature; but, on the other

=

hand, if a difference exist, we know that the number of degrees which the wet bulb is lower than the dry bulb, indicates the quantity of heat that has been used in evaporation: thus, if the two thermometers stand at 60°, the surrounding atmosphere is in a state of saturation, and therefore incapable of taking up any more moisture; evaporation is suspended, and no extra heat required; the wet bulb in this case, therefore, having no demand made upon it for its caloric, indicates the same temperature as the dry bulb. When, however, the dry bulb stands at 60°, and the wet bulb at 41°, then we infer that the air is far from saturation point; and from the accurate calculations and tables of James Glaisher, Esq., we know that 3.95 grains of vapour are required to saturate a cubic foot of air under such circumstances, and that the actual amount of moisture in this quantity is 1·92 grs. 1·92 +3·95=5·87 grs., which is exactly the weight of vapour in every cubic foot of air when both the thermometers stand at 60°. This illustration has been given in order to show the distinct relation that obtains between the hygrometric state of the air, the amount of evaporation of water from moist bodies, and the expenditure of heat in this conversion of water into vapour. Now if the atmosphere be loaded with moisture, it not only interferes with the cutaneous exhalation, but it has a similar effect on the pulmonary mucous membrane, which exhales about twenty ounces of vapour in the twenty-four hours. The reader must not forget that the skin is a respiratory organ, and adds its quotum to the maintenance of the animal heat, as has been found in the experiments of MM. Becquerel and Breschet, who glazed the skins of shaved rabbits, and found, although the cooling process of the evaporation of the perspiration was stopped, that the temperature of the animals fell from 100° to 76° in about an hour. So important a feature in meteorology as the indication of moisture in the atmosphere, could hardly escape the observation of the antient physicians; and on referring to their works, we find that they were all alive to the

influence that it exerted on the healthy as well as on the diseased body. Galen, in his Commentary on the Epidemics of Hippocrates,* seems to draw a line between the effects of moist and dry weather: the former, he says, is apt to affect the bowels, producing belly fluxes (Koiλins pvotes), and the latter the renal organs. It will be well to bear in mind this remark, for it is one of great importance, and quite pertinent to the present subject. In hot moist conditions of the air,-for instance, during the hot and rainy seasons in Bengal,-there is great vascular and nervous excitement, the blood is determined to the surface, and whilst, during the rainy season, the atmosphere is loaded with moisture to saturation, the cutaneous exhalation, instead of evaporating, and cooling the body, pours out without relieving the intolerable heat: this inordinate aqueous discharge increases the density of the blood, renders it a stimulating fluid, and at the same time the body becomes susceptible of the least impression of cold; the air, from its saturation with moisture, becomes less vivifying, being filled with emanations from decomposed animal and vegetable matters; in fact, as Mr. Ranald Martin observes,† it becomes "a tainted vapour bath," to the malarious influence of which the body has become highly susceptible. To the stimulating properties of the blood, deprived by excessive transudation of more than its usual amount of water, and of less of its hydrocarbon, are referred by Dr. C. J. B. Williams the disposition to liver complaints, dysentery, and cholera. Now it must be evident to the reader that the meteorological conditions conducive to so severe a form of dysentery as that just referred to, are never observed in England, and that, in fact, the deaths from this disease, when compared with the mortality arising from many others, are really very few, although pretty constant in their average.

Temperature. I think that we may safely infer, from what Hippocrates has said of this constitution, that there was no great

* Gal. Op. ed. Kühn, vol. 17, a, p. 32.

+ Op. cit.

amount of hot weather during the six seasons; we therefore cannot ascribe to the temperature the prevalence of dysentery: in fact, no disease can be said to be dependent for its development on only one or two causes; it is the combination of conditions well blended together that gives an impulse to the disease-germ, and renders the animal system fit for bringing it to maturity. In such a concentration, one element may be more or less prominent at any particular season, when certain diseases prevail, but this is no reason why they should be hastily attributed to this one cause, because it happens to be the most conspicuous; although there can be no doubt that it may have had its share in the preparation of the poison. In the germination of seeds, heat, moisture, and access to air, are necessary; but should any one of these conditions-moisture, for instancepreponderate, would it be reasonable to ascribe to this one cause alone the shooting forth of the plumule and radicle? We must look to the union of conditions, if we desire to fathom the origin of disease, and not allow ourselves to be led away by what superficially appears to be the most active agent connected with it.

Considering the small number of deaths which weekly take place from dysentery in the metropolitan districts, it may be thought that I have dwelt too long on this disease; but I thought that I could not pass it over without mentioning some of the few meteorological conditions that generally precede and accompany its attacks upon our countrymen in the East, where we have seen that excessive heat and moisture play so prominent a part in its production.

In London, the weekly average of deaths from dysentery ranges from 2 to 9; and although the higher number is more frequent as the temperature of the year rises, yet there is not a sufficient swelling of the numbers to justify us in attributing it altogether to the increased heat, but rather to that peculiar condition of the atmosphere resulting from a combination of causes, which seems so obnoxious to the alimentary canal; for, as