These conditions may be considered together, for as factors in the causation of disease they usually go hand in hand. A damp house is commonly a cold one, and a cold house is liable to be a damp one, because the condensation point of water is directly dependent on temperature.

The maladies produced by cold and damp are different from those which we have previously considered. Amongst the most important are diseases of the respiratory organs. The too familiar "common cold" is a complaint the causation of which is not yet thoroughly understood. In many, perhaps in all, cases it is a truly infectious disease, as is shown by its capacity for running through a household; but the specific microbe is not at present certainly recognized, Nevertheless chill, and especially sudden changes of temperature, are universally admitted to play an important part in its production, and this very rightly, the effect of these being to depress vitality and diminish the powers of resistance against infection. The same is true of pneumonia. It is known that this disease depends upon a specific microbe - the Diplococcus pneumonia, - but the effects of chill upon its production are undoubted, and are to be explained in the above manner. Pleurisy and bronchitis are other respiratory diseases which have a definite relation to cold and damp.

Two diseases, however, stood out pre-eminently as favoured by the above conditions: they are phthisis and rheumatic fever. In the production of phthisis cold alone seems to play an unimportant part, save in so far as the production of catarrhs increases the liability to infection by the tubercle bacillus. An equably cold but dry climate does not appear to conduce in any way to phthisis, except by leading to deficient ventilation. Damp, however, has been shown by Buchanan in this country and by Bowditch in America to play a very important part in predisposing to the disease, dampness of soil leading to a high phthisis-mortality, which in many cases has been materially reduced by artificial drainage. A contemplation of the map of phthisis-mortality in this country, prepared by Havilland, illustrates strikingly the effects of climate in this direction. The combination of cold and damp is probably more injurious than damp alone; but it must be remembered that they are only two of the conditions which lead to the disease, which itself invariably depends upon infection by the tubercle bacillus. We do not know whether rheumatic fever is a bacterial disease or not, but there is no question as to the close relation which exists between its prevalence and conditions of cold and damp. Sleeping in a damp bed is a not uncommon cause of the complaint, and cold and damp in the house are probably as directly connected with it as coldness and dampness of climate. The chronic forms of rheumatism and allied diseases are notoriously aggravated by these conditions. Neuralgias often are to be traced to similar causes. Malaria has almost disappeared from Britain, but in other countries the blood-parasite which is known to be its cause is most commonly present in damp and low-lying localities.