There is in the long run no simple influence so conducive to health of mind and body as a proper amount of physical exercise under the proper surroundings. The lungs feel the effect of exercise more than any of the organs. Smith found out by experiment that every exertion which he made increased the amount of air he inspired. He represented the amount of air which he breathed in when lying down as one. When standing, he took in one and one-third times as much. When walking at the rate of four miles an hour, fives times as much. When walking at the rate of six miles an hour, seven times as much. The increase is shown, perhaps, in a more striking way by Parker, estimating the different amounts in cubic inches. The flow of blood through the lungs is much less rapid when one takes little or no exercise; and the carbonic acid will not be removed from the system in so thorough a manner. If a man then is obliged to lead a life which deprives him of the chance of getting a fair amount of physical exercise, he should, if he wishes to keep himself in health, reduce the amount of carbon which he has been in the habit of introducing into his system. Fats and alcohol should be tabooed. The need of fresh air in all exercise is very great, and this is the great objection to all in-door exercise. The actual results of impure air arising from too many people in one place, is shown by the sufferings of those confined in the "Black Hole" of Calcutta. Huxley has computed that a man needs 23,000 cubic feet of air every day, that his excretions of carbonic acid may not pollute the air. Pleurisy not only affects the lungs but the diaphragm, which is the principal agent in drawing air into the lungs. The enlargement of the pleura forces the air out of the air cells, thin walls are brought into contact with each other, and the whole lung in an airless condition may be pressed into the back part of the chest alongside of the back bone, where it lies as useless, as far as breathing is concerned, as a strip of leather. The same results may follow from the destruction of the elastic fibre of the lung, which takes such an active share in driving out the air expiration. Impurities in the air are breathed in and cause fevers. The diseases which result from trouble to the respiratory organs are almost innumerable. It is estimated that of those who die before their sixth year of existence, one-fourth die of respiratory troubles. Of those dying from fifteen to twenty-one, half fall victims to breathing troubles. Consumption only carries off nearly half of those who die between the ages of twenty-five and thirty-five. These computations are made from a million people who have lived in the vicinity of Liverpool. It is our duty to do all we can to prevent this terrible march of the respiratory diseases. In Massachusetts and in certain English towns, owing to more prudent and sagacious living, the death rate has been materially lowered; in some cases as much as fifty per cent. The number of picked men in the English army who have been obliged to go into hospitals owing to respiratory diseases, is remarkable. When consumption once takes hold of a man, it is almost impossible to shake it off. Its best cure is prevention. Fresh air is therefore essential, and plenty of exercise to keep the blood pure and the flow rapid.