=Eugenics and tuberculosis.=--It would not be correct to say that the old view of consumption regarded it as hereditary. In this and a hundred other matters, medical, astronomical, or what we please, if we go back to the Arabic students, or further, to the Greeks, we are lucky enough to find sound observation and reasoning. Many quotations might be made to show that the infectious nature of tuberculosis was recognised long ago, just as the revolution of the earth round the sun was recognised a millennium and a half before Copernicus. But the view of our more immediate fathers was that tuberculosis is a hereditary degeneration, and the medical profession proclaimed with no uncertain sound the hopeless and paralysing doctrine that an almost certain doom hung over the children of the consumptive. Then, in memorable succession, came Villemin, Pasteur, and lastly Koch, with his discovery of the bacillus in 1882. The doctrine was then altered in its statement. There was, of course, no choice in the matter, since it was easy to show that not one new-born baby in millions harbours a tubercle bacillus; so all-but-miraculous and, rightly considered, beautiful are the ante-natal defences. It was taught, then, that we inherit a predisposition from consumptive parents, that the bacillus is ubiquitous, and that variations in susceptibility determine the incidence of the disease in one and not in another. It was lightly assumed (simply through what may be called the inertia of belief) that these variations in susceptibility were hereditary; but we are wholly without evidence that the hereditary factor counts for anything substantial, even assuming that it appreciably exists at all. These differences, so far from being inherent, may be _most palpably_ acquired. Under-feeding, alcohol, and influenza, let us say, will adequately prepare any human soil. Furthermore, we are learning that the bacillus is nothing like so ubiquitous as used to be supposed. Tuberculosis is now sometimes described as a dwelling disease. It might probably be described with still more accuracy as a bed-room disease, or a bed-room and public-house disease. It has been evident for many years past that the more we learnt about tuberculosis the less did we talk about heredity; and in one of the most recent authoritative pronouncements[48] upon the subject, the lecturer did not even allude to heredity at all. Many readers will be up in arms at once with apparently contrary instances; and much labour may be spent in the mathematical analysis of statistical data--as that of cases where a father and a child have tuberculosis. But suppose the father kissed the child? What have you proved regarding heredity? No mathematics can get more out of the data than is in them.