nature (sebaceous complexioned). But dysentery was not the only disease mentioned by Hippocrates, for he adds lientery, tenesmus, bilious diarrhoeas. Galen, in his Commentary on this passage (vol. xvii. u, p. 101), attributes the prevalence of these alvine affections, first of all to the cold, which had the effect of condensing the skin and thickening the animal juices; and, secondly, to the moisture, which not only did not admit of exhalation of the redundant humours from the surface, but actually increased their amount; consequently an accumulation took place in the system, for which nature found an outlet either through the liver or the bowels. Hippocrates well remarks that cold acts more energetically and promptly on weak moist subjects, and on women, than on the robust; and thus he explains how it is that such persons are so liable to dysentery during cold weather, for their cutaneous secretion is lessened, the vessels of the surface are constricted, the blood is thrown internally, and this loss of balance in the circulation, instead of being followed by a healthy reaction, as in robust subjects, is the first element of congestion, which often terminates in a flux. It must be remembered that some of the affections enumerated above, such as tenesmus and strangury, were symptoms of the severe form of dysentery, and not distinct complaints. We shall first give an outline of the opinions of ancient and modern authors with regard to the influence of the seasons on this disease, and then proceed to analyse the relation that its prevalence bears to the meteorological condition of the region at the time of its being an epidemic. The Season in which Dysentery generally occurs.-On referring to the table of the Second Constitution, we find that it prevailed during the summer and autumn (κατὰ δὲ θέρος καὶ φθινόTwрov).* Hippocrates also enumerates it among the diseases of autumn (Aph. sec. iii. xx.) Aretæus† remarked that dysentery Hippocrates, ed. Kühn; Littré, vol. ii. p. 616. + Ed. Kühn, p. 161. D prevailed most in summer, next in autumn, rarely in spring, and least of all in winter (γίγνεται δὲ θέρεος ὥρῃ, δεύτερον φθινοπώρου, hooov hрos, úklσta xeiμ@vos). Dr. Joseph Brown's* experience has led him to observe that dysentery is generally most prevalent during the latter end of summer and autumn, when the alterations of temperature are sudden, and especially where there is considerable discrepancy between the heat of the day and the night. Mr. J. Ranald Martin, in his interesting papers† on the Disorders and Diseases of Tropical Climates, says that dysenteries become more frequent, severe, and complicated, in the rainy months that succeed to the hot season in the East: further on, he adds that dysenteries, frequently complicated with hepatic disease, are among the acute diseases of the cold season. Galen merely quotes the opinions of Hippocrates, who, besides ranking dysentery among autumnal diseases, remarks that in the spring, and especially in the summer, men are seized with dysenteric affections! (οι ἄνθρωποι τοῦ ἦρος καὶ τοῦ θέρεος μάλιστα ὑπὸ τῶν δυσεντεριῶν ἁλίσκονται). We shall now give the result of the Registrar-General's statistics on this subject, so far as the metropolitan districts are concerned, and compare them with the preceding remarks (see table in following page). vñò The totals place the different seasons in much the same order as we have seen above the experience of Aretæus led him to adopt; the summer invariably proving to be most fatal, and the autumn next. Statistics, however, seem to show that the spring is rather less obnoxious to persons labouring under dysentery than the winter; the mean for the different quarters of the eleven years being— Summer, 61-10; Autumn, 41-8; Winter, 22.9; Spring, 19'6. Diarrhoeas are mentioned as having been prevalent during the summer and autumn of this second constitution, and it Encyc. Practical Med. vol. i. p. 658. † Lancet, vol. i. and ii. 1850. Galeni Op., Kühn, vol. vi. p. 690. 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 |