EXDEMIC AXD EPIDEMIC DISEASES.] 



METEOROLOGY. 



1205 



case, a series of identical and progressive changes in the 

 atmosphere of an infected place could be determined as 

 invariably preceding the outbreak of the disease, the 

 difficulties of this interesting subject would be lessened, 

 if not entirely removed. But no such direct connection 

 has yet been established ; which may be partly owing to 

 the deficient method of observation adopted until within 

 late years, and also to the great obscurity of the causes 

 which always precede, but often escape our notice, 

 despite of every endeavour to discover them. These 

 difficulties have already been named by Dr. Scoffern at a 

 previous page ;* and we only re-enter on the subject for 

 the purpose of pointing out, more definitely, the facts of 

 the case, which have hitherto been but incidentally men- 

 tioned, and to supplement, in some particulars, the 

 remarks which have been offered. 



Wherever an endemic or epidemic prevails, it will be 

 generally found that the temperature and moisture of 

 the district have much to do with it, and that they are 

 either in excess or deficiency, according to the nature of 

 the complaint. Such diseases are generally of two 

 kinds ; namely, those attacking either the organs of 

 respiration or digestion. Amongst the former may be 

 instanced influenza, bronchitis, and diseases of the lungs 

 in general ; and, of the latter kind, are diarrhoea, cholera, 

 &c. : another class, that of thu purely febrile type, has 

 specific characters 'of its own. 



In a hot and moist atmosphere, the entire human 

 system generally suffers from debility ; but a dry air, if 

 e.ther very hot or cold, and not long continued in, produces, 

 comparatively speaking, but little inconvenience. Thus 

 it is no uncommon occurrence for the temperature in 

 Canada to fall to 20 or 30, and, in the Arctic regions, 

 to 60 or 70 below zero, where, so long as the air is still, 

 no harm endues ; on the other hand, a temperature of 

 200 and 300, with dry air, is quite harmless to the 

 human body exposed to it. In India, Africa, and the 

 West Indies, where, however, great moisture generally, but 

 not always, accompanies a high temperature, the utmost 

 danger exists to Europeans ; the liver, organs of digestion, 

 c., becoming affected ; and hence a predisposition to 

 diseases of all kinds is generated ; the body, in fact, 

 enters, in respect to nearly all its organs and func- 

 tions, into abnormal conditions, and disease is, generally 

 speaking, the universal consequent. 



In our own country, the sudden changes of tempera- 

 ture, with a comparatively moist atmosphere, are 

 frequently productive of serious consequences, although 

 those changes are slight in comparison with such as con- 

 stantly take place, even within a few hours, in the Canadas. 

 But with us, as in some parts of India and other coun- 

 tries, the conducting power of the moisture is the cause 

 of injury ; hence a hot summer in England i.s more 

 intolerable to a West Indian, and a cold winter to a 

 Kussian, than such seasons are in their own countries ; 

 because there, on the average, the air is much drier, and 

 therefore conducts heat, both to and from the body, 

 much more slowly. The most healthy climates are, 

 generally speaking all other thinys being equal those 

 that are the driest : hence, in some parts of Chili, on the 

 plains in the Andes, where the air is very dry and 

 bracing, an age of about 100 years is by no means 

 uncommon in individuals ; and even that is very often 

 greatly exceeded. 



In numerous cases, therefore, we may partly account 

 for the prevalence of disease in districts, or at certain 

 seasons, by a rapid change in the conditions of tempe- 

 rature and moisture. In some parts of the tropical and 

 sub-tropical zones, the duration of the rainy and hot 

 seasons, and their changes, afford just such circum- 

 stances as are likely to produce disease in the 

 human subject ; for the skin, ever casting off, by its 

 millions of pores, the watery humours and effete matter 

 from the system, is often suddenly checked, or unduly 

 stimulated in its action; and hence febrile symptoms, 

 and inflammation of the organs of respiration and 

 digestion, are immediately induced, and dysentery, in 

 it* worst forms, becomes prevalent and fatal. 



See ante, p. 11M. 



In the remarks which we have already made on the 

 meteorological influence of drainage, at page 1186, we 

 have pointed out some of the evils arising from a moist 

 climate, either when hot or cold, and also from local con- 

 ditions of the same kind : several countries are also 

 named in which these conditions are always present. 

 In such places, the increase or check of perspiration so 

 commonly occurring, is quite sufficient to account for the 

 various diseases endemic in them. But, in many places, 

 there can be no doubt that the outbreak of either an 

 endemic or epidemic, may be due, directly, to the 

 presence in the air of poisonous exhalations, which 

 have an immediate action of their own on the human 

 system, or may act conjointly with changes of tempe- 

 rature and moisture. The visitations of cholera in this 

 country, during the last thirty years, have been highly 

 instructive to the scientific observer, in respect to such 

 causes ; and perhaps, incidentally, have done more to 

 improve the general health of the nation, than would 

 have resulted had not their fatal effect stimulated us to 

 adopt universal sanitary measures. 



A careful observation of meteorological conditions 

 which prevail preceding to, and during an outbreak of 

 cholera, generally records a comparatively high tem- 

 perature, and a moist and stagnant atmosphere. Diseases 

 of the diarrhoea kind are rarely, if ever, prevalent 

 during periods of high wind ; and, on the other hand, 

 they are alicays most virulent and fatal in places where 

 a constant change of the atmosphere of the locality does 

 not take place. During the last visitation of cholera in 

 London, Lambeth and Southwark a great portion of 

 which districts is below the level of the Thames at high 

 water, and constantly very damp suffered most seriously 

 and fatally from the disease ; and, generally speaking, 

 those districts which, like the above, were badly drained, 

 and not exposed to the natural ventilation produced by 

 free access of natural aerial currents, were plainly marked 

 as infected and dangerous localities. 



Another and important quality of moist air, to 

 which but little attention has been directed, is the power 

 of aqueous vapour, in a suspended state, of holding in 

 solution gases, &c., and of thus carrying witli it exha- 

 lations of all kinds, in a form ready for assimilation 

 with the human system. Dry air may be mixed with 

 other gases, which, in most cases, will readily diffuse 

 themselves through it ; but moist air, by reason of the 

 water it contains, becomes a much more effective poison- 

 carrier. Hence arises the peculiar smell of marsh lands 

 in autumn; of water in which "greens" have been 

 boiled, &c. : and, in each of these instances, the gases 

 evolved during the chemical decomposition of the vege- 

 table substances, are carried off in a volatile form, and 

 are thus frequently detected by the sense of smell. 

 With respect to the nature of these volatile poisons 

 thus evolved, little or nothing is known. We have 

 already referred to this subject in the Section on Che- 

 mistry ;f stating that it has hitherto been impossible to 

 detect the active poison thus floating in the air, with the 

 exception of the sulphuretted hydrogen, to which some 

 have attributed, together with a carburetted hydrogen, 

 the chief influence of miasmatic effluvia. The great 

 attention which has lately been paid to detecting the 

 presence of free ozone in the air,J may eventually be 

 rewarded by a further insight into this interesting but 

 obscure subject ; at least, it is in that direction alone 

 that any hope for a solution of our difficulties can be at 

 present cherished. 



In tropical countries, where a hot-moist air always 

 prevails, the climate at the mouths of rivers, which gen- 

 erally enter the sea by a "delta" consisting of low-lying 

 marsh lands, is almost invariably unhealthy, and some- 

 times uninhabitable. The periodical overflow of the 

 rivers during the rainy season, inundates the land, often 

 over a very extensive area. Vegetation progresses 

 rapidly when the stream subsides ; and, eventually, the 

 decomposition of the plants produces malaria of an ex- 

 ceedingly fatal character. The atmosphere is sometimes 

 poisoned even far into the interior, by the sea-breeze 

 i Sc ante, pp. 428, 429. See ante, pp. 1187, 1188. 



