In the last chapter we saw that while selection is an evident and powerful factor in the production of racial change, there is but slight and in many cases questionable evidence that acquired characters are ever transmitted. During their lifetime a man or woman may be subject to the most varied conditions, and yet the quality of his or her offspring will not be affected by these conditions except in cases where impoverishment or poisoning of the blood has ensued, thereby enfeebling his or her reproductive cells. These facts have not been gained by a study of the lower animals alone, for most researchers have kept man in view, while others, like Malthus and Galton, have confined their observations almost exclusively to the human kind. In this chapter we shall see how these generalisations are borne out by the study of disease, and we shall see what effect the modern methods for the treatment of the sickly and feeble are having upon the race. We moderns as individuals have many advantages over those who have gone before us; we owe to the untiring energy of our ancestors the facilities for travel, the pleasures of accumulated music and literature, etc., but among these hundreds of advantages we possess none are more marked than those we owe to the scientific followers of the profession of medicine, the application of whose learning gives in our day to the less robust a possibility of life and happiness they never had before. _Preventive Medicine._ The words “mederi,” to heal, “medicus,” the healer, and “medicina,” the remedy, indicate pretty clearly the almost superstitious feeling current in early times regarding the attributes of the medical man; but physicians have in more recent years begun to doubt in some measure of their power to cure disease when once established. With increased knowledge, and with growth of professional acumen, the limits of this power are more clearly seen, and the solution of a metallic salt, or decoction of a herb is now withheld when at one time it would have been administered with the fullest confidence. With this healthy scepticism as to their power to cure has come very certain and exact knowledge of how to prevent, and preventive medicine has recently exercised an influence upon disease and upon mortality which is unique in the history of humanity. But while the benefit of our changed and more healthy surroundings are to the advantage of us all individually, we shall have to consider whether as a people we shall in the long run be the better for this change, or, on the other hand, whether in obtaining this individual advantage we are not imperilling the vigour of the race. _Micro-organisms of Diseases and their Extermination._