The mere immediate or exciting causes of consumption, those which determine the deposition of tubercles, have usually been attributed to irritants acting locally on the bronchial tubes or on the lungs, whether occasioned by inflammation of these parts or by the mechanical action of irritating bodies upon them. The result of the latest investigations on this subject leave no doubt that the influence exerted in this way has been greatly exaggerated. Pneumonia and bronchitis, the two diseases hitherto regarded as the most frequent forerunners and pro ducers phthisis, have been shown by M. Louis to exert no more influence in its production than any other disease. They may indeed occasionally hasten the development of tubercles, but they exert no specific effect, and they act only as remote cause; in impairing the health generally. These conclusions of Louis, which have been deduced from his own observations in hospital practice solely, receive ample confirmation from the admirable Statistical Reports of the Registrar-General and Major Tulloch, which we have before referred to. The popular error of attributing consumption to cold, the breaking of a blood-vessel, &e., has probably originated from mistaking the effect for the cause. We have shown in a former part of this article that cough and hiemoptysis are among the earliest symptoms of tuberculous lungs.
With regard to mechanical irritants, as dust of various kinds, noxious gases; smoke, &e., "no opinion has been more prevalent," observes Dr. Cowan, "than that those who are exposed to the inhalation of the dust of vegetable, mineral, or animal substances, are peculiarly liable to phthisis ; and in the supposition that consumption was essentially a disease of the lungs, and in the great majority of instances the result of bronchial inflammation, no conclusion was more natural or mere probable. But once remove from the mind the impression of a neces sary connection between bronchitis and tubercles, and we feel per suaded that the examination of the evidence brought forward on the subject of dust will terminate in the conviction that this agent exerts at most but a very secondary and unimportant influence in the pro duction of phthisis." The mortality among the workmen in some of our manufacturing towns is usually brought forward in support of the doctrine of mechanical irritation. Dr. Knight, of Sheffield, informs us that there is not an example of a polisher of forks reaching his 36th year, nor do the artisans in other departments attain a much greater age. But it must be recollected that many of these men work sixteen hours a day in a close atmosphere and confined posture of body, two conditions which contribute perhaps more than any other to the increase and production of phthisis. Nor has the mortality been diminished by the use of magnets, wire masks, currents of air, and moisture, which have been successively tried for the purpose of arresting the metallic particles. In the eases of 887 quarrymen, 557 stone cutters, and 160 marble-workers, all of them occupations involving the Inhalation of dust, M. Benoiston found the proportion of phthlsis was less than the general average ; but then these are employments carried on in the open air. Dr. Lombard, whose researches are founded on a total of 4300 deaths from phthisis, and 54,572 individuals, exercising 220 different occupations, found, by a comparison of all the professions carried on iu the open air and in workshops, that the proportion of deaths from phthisis was double among the latter; and this propor tion increased as the apartments were close, narrow, and imperfectly ventilated.
Mr. Watson, a surgeon of Wenlockhead, a mining district, informs us that, out of 74 men working during four or Ave months for sixteen hours daily in a mine where a candle burnt with difficulty, not one was attacked with any pulmonary affection. But whether from the inhala tion of any noxious gases or from other causes, it is certain that in the majority of the mining districts of this country the mortality from phthisis is high. The number of males attacked by this disease in
Cornwall exceeds that of the females in the ratio of 170 to 140, and in the mining parts of Staffordshire, Shropshire, and Worcester, in the ratio of 203 to 191; while in the non-mining districts of Staffordshire and Shropshire, and in the county of Cheshire, the ratio is 656 males to 796 females.
The influence of smoke, when unoombined with other agents of injurious tendency, may, we think, fairly be called in question. In Leeds, which is certainly the most smoky place in the whole kingdom, the mortality of females from phthisis is below that of most of our large manufacturing towns, and is not much above the average for the whole of England and Wales. In London likewise this is the case, and in nearly the same proportion.
A moist and changeable climate was long regarded as among the most active causes of consumption ; and Great Britain, whose climate combines these two conditions in a remarkable degree, has been looked upon as such a nursery for phthisis, that cur facetious neigh. hours on the other side of the Channel have styled it " La Maladie Anglaise." Indeed the notions of atmospheric vicissitudes, dampness, and consumption, seem almost inseparable. However, these opinions have been and still are undergoing a severe scrutiny ; and the evidence which we at present possess on the subject tends very strongly to dis prove their correctness. Moisture and climate, like all other agents, act either locally or generally; popular belief has attributed their pre Burned prejudicial effects to local action. They tend, it is said, to produce catarrhs and coughs, and consequently consumption. We need scarcely allude again to the fallacy of this opinion. We are in possession of little information on tho mode in which climate operates to the production of phthisis. That the disease prevails to a much greater extent in some climes and localities than in others, is an indis putable fact ; but it is no less certain that its prevalence is net confined to countries of variable temperature, for many of such countries suffer in a much less degree than those whose thermometric range vanes little throughout the year. is phthisis contagious if This is a question which has been often discussed, and numerous are the testimonies both (when we consider the relations of beat and light, thus taken together to the other physical forces) that they in reality are the initiating forces of nature, and that when they seem to be produced by the other forces, they are, in fact, merely evolved from them. Much evidence might be adduced from natural phenomena, and the results of experi mental research, in favour of this view of the subject. But heat and, light appear to have the power of producing the other forces from the moment of their own origination ; and the broad induction from the actual state of our knowledge of their radiation Is that they originate In union, and—in an absolute aense—are inseparable, both being always present, though in variable proportions to each other ; with, at the same time, a certain reciprocity of presence and activity, the one taking the place of the other to the extent, or in the degree, to or in which the other is shunt. The recent experimental researches on radiation of M. Foucault, Mr. Balfour Stewart, and Professor Kirchhoff (' Pr c. of Roy. Soo.: and Phil. ralag.: 1860, &c.), sectn to furnish irrefragable evidence on this point; and a remarkable example of the reciprocity here alluded to, in the relation of animal heat and animal light to each other, was pointed out by Mr. Brayley, in a lecture delivered at the London Institutiou in 1833, the substance of which was communicated to the Natural History section of the British Association in that year, but not printed till 1835, when it appeared in ' Phil. Mag.,' third series, vol. vi. lip. 241-247.