cannot be doubted, and this in spite of the greater attention which is now-a-days paid in some places to ventilation; for the best ventilation that exists in such houses as we inhabit, though it may help to maintain the vitality by ensuring an abundant supply of unvitiated air, is not of a kind to sweep the pathogenic organisms from the dwellings.
The conditions under which we live are such that, normally, every individual amongst us is exposed to infection, that is, we all at one time or another enter rooms inhabited by tuberculous patients; but such has been the evolution of resisting power in our race, that only one-seventh of us perish from consumption, while six-sevenths of us live immune to the disease, or recover from it, and die from other causes. A notable fact in this connection is the often evenly-balanced nature of the struggle between the microbes and the phagocytes. Many of us are resistant under almost any circumstances; many others easily contract the disease, and fall a rapid prey, even under circumstances the most unfavourable to it to be found in our land; but very many others exist in the border space between immunity and susceptibility. Such people, when their vitality is lowered, or under other circumstances favourable to the bacilli, contract the disease, but when their vitality is raised, or when the environment becomes less favourable to the pathogenic micro-organisms, defy it, or, if they are already diseased, recover. Even when they do not recover the disease usually runs a prolonged course in them; there is a lengthened struggle between the microbes and the phagocytes, and we then behold the phenomena of chronic phthisis. Laennec said that a patient does not die of his first attack of tuberculosis; that is, a patient of the highly resistant type, which is the normal in our race. Less resistant individuals, who have lapsed back to the ancestral condition of greater susceptibility, undoubtedly
