The effects of bad ventilation, it need not be pointed out, are chiefly manifested in consumption, the disease by which the greatest slaughter is committed. The causes of fever are comparatively few and prominent, but they appear to have a concurrent effect in producing consumption. The investigation of the whole of the contributary causes to the production of the immense mass of mortality occasioned by that disease, would be beyond the time or means allowed for the present inquiry; but defective ventilation and defective management in respect to changes of temperature, are causes everywhere apparent amongst the labouring classes. The effects of good ventilation, as a single cause of the prevention or alleviation of disease, are nowhere so clearly manifest as in their effects on hospital treatment. What Dr. Bisset Hawkins states in respect to the sanitary measures necessary to ensure successful treatment in hospitals, may be stated in respect to common dwellings as well as places of work. “Next to the influence of national causes, the mortality of hospitals is most affected by position and internal economy. These circumstances appear more powerful than even the various merits of practice; and, happily for mankind, they are advantages of a definite nature, easily comprehended, and, of late years, generally demanded. The case was formerly very different, when a singular prejudice or indifference existed in respect to ventilation. At the Leeds hospital no case of compound fracture, nor of trepan, survived. At the Hôtel Dieu, of Paris, compound fractures were also almost always fatal, and few survived amputation. The system which will bear improper air with impunity during health becomes keenly susceptible of its mischief when diseased, and a change of air will often restore where the strictest diet has failed. Mortality is seldom to be assigned to the influence of bad practice, which, probably, does not often destroy life. An accomplished friend made particular notes on the comparative mortality under three physicians in the same hospital; one was expectant, one tonic, and the other eclectic. The mortality was the same, but the length of the disorder, the character of the convalescence, and the chances of relapse were very different.