cause only some forty-five thousand, notwithstanding the great increase of population. Reckoned per million of population, this represents only 1,635, instead of the 3,880 of fifty years previous. The decrease, moreover, had been progressive during all that time through each quinquennium, and was no doubt due to general sanitary improvements, but not to measures directed especially against tubercular disease. The ventilation of work-rooms, restriction of hours of labour and of the ages at which children were allowed to work, and other kindred measures have acted beneficially against all diseases which like tubercle best take root in those already weakened in constitution. The war waged was with disease in general, or perhaps it may be better expressed as an attempt to lessen the predisposing causes of disease, while the knowledge of the exciting cause was, in the case of tuberculosis, absent. Tuberculosis, as its name indicates, is characterized, as regards its pathology, by the formation in the affected organs of the body of small masses of abnormal material called tubercles. These tubercles vary in size. In following the process of the disease one may note that, at first hardly perceptible, these little masses increase in size, and there gradually appears in the centre of each a yellowish colour, due to the death of the tissues in this part, and the formation from them of a cheesy substance. These masses continuing to grow coalesce with each other. After a certain stage is reached the centre of the cheesy mass begins to soften, and an abcess is formed, which finds an outlet—frequently through the normal passage of the affected organ; in the case of the lung, through the air-passages. In this way the process of excavation goes on, and a progressive case leads to the gradual destruction of large areas of the affected organ. I go into these details to explain that until recent times a satisfactory explanation was wanting as to what caused these tubercles, which are essentially the disease. Now we know that they are due to the presence of a special germ, which finds a suitable soil for developing in those whom we in consequence call predisposed to consumption. No case arises of itself without the entrance of the tubercle germ into the body, and without its finding there a suitable resting-place. The knowledge that tubercles depended on a special disease germ was arrived at only after innumerable researches, and for many years the results of these researches provided only material for dispute among those making them. One of the first steps towards the proof of the communicability of tuberculosis was the production of it by the injection of cheesy material from the tubercles into the bodies of such animals as guinea-pigs and rabbits. Later it was shown