But the consoling fact remains that even of such children, providing, of course, as usually happens, that the other parent--husband or wife--is sound and sane, not more than ten or fifteen per cent would probably become insane. In other words, insanity is acquired and the result of individual stress and strain at least five times as frequently as it is inherited. We have absolutely no rational or statistical basis for gloomy predictions that, at present rates, within a couple of centuries more, we shall all be shut up in asylums with nobody left to support us and pay the taxes. The apparent increase of insanity of recent decades is probably only "on paper," due to better registration. To put it very roughly, probably ninety-eight per cent of us are so born, thanks to heredity, that the possibility of our becoming insane, even under the severest stress, is almost infinitesimal. Of the two per cent born with this taint, this possible tendency to mental unbalance, only about one-tenth now become completely insane,[1] and this percentage might be greatly diminished by general sanitary improvements. Our alienists now claim that, by checking the reproduction of the obviously unstable, and careful hygienic treatment and training of the predisposed two per cent, insanity is almost as preventable as tuberculosis. [Footnote 1: The proportion of registered insane in civilized countries to-day ranges from two to three per 1000 of the population.] In fine, from all the broad field of pathology, the mists of tradition which have dimmed the fair name and reputation of heredity are slowly but surely lifting, until we now behold it, not as our worst enemy, but as our best friend in the prevention of disease and the upbuilding of the race. CHAPTER III THE PHYSIOGNOMY OF DISEASE: WHAT A DOCTOR CAN TELL FROM APPEARANCES It is our pride that medicine, from an art, and a pretty black one at that, originally, is becoming a science. And the most powerful factor in this development, its indispensable basis, in fact, has been the invention of instruments of precision--the microscope, the fever thermometer, the stethoscope, the ophthalmoscope, the test-tube, the culture medium, the triumphs of the bacteriologist and of the chemist. Any man who makes a final diagnosis in a serious case without resorting to some or all of these means is regarded--and justly--as careless and derelict in his duty to his patient.