The knowledge of the causation of disease by bacterial and protozoic parasites is a thing which has come into existence, under our very eyes and hands, within the last fifty years. The parasite, and much of its nature and history, has been discovered in the case of splenic fever, leprosy, phthisis, diphtheria, typhoid fever, glanders, cholera, plague, lock-jaw, gangrene, septic poisoning (of wounds), puerperal fever, malaria, sleeping sickness, and some other diseases which are fatal to man. In some cases the knowledge obtained has led to a control of the attack or of the poisonous action of the parasite. Antiseptic surgery, by defeating the poisonous parasite, has saved not only thousands upon thousands of lives, but has removed an incalculable amount of pain. Control is slowly being obtained in regard to several others among these deadly microbes in various ways, most wonderful of which is the development, under man’s control, of serums containing antitoxins appropriate to each disease, which have to be injected into the blood as the means of either cure or protection. But why should we be content to wait long years, even centuries, for this control, when we can have it in a few years? If more men and abler men were employed to study and experiment on this matter, we should soon make an end of all infectious disease. Is there any one, man or woman, who would not wish to contribute to the removal from human life of the suffering and uncertainty due to disease, the anguish and misery caused by premature death? Yet nothing is done by those who determine the expenditure of the revenues of great States towards dealing adequately with this matter.[11] 15. THE INCREASE OF HUMAN POPULATION. Whilst there is a certainty of Man’s power to remove all disease from his life, a difficulty which he has already created for himself will be thereby increased. That difficulty is the increase of human population beyond the capacity of the earth’s surface to provide food and the other necessities of life. By rebelling against Nature’s method, Man has made himself the only animal which constantly increases in numbers. Whenever disease is controlled his increase will be still more rapid than at present. At the same time no attempt at present has been made by the more advanced communities of civilized men to prevent the multiplication of the weakly or of those liable to congenital disease. Already something like a panic on this subject has appeared in this country. Inquiries have been conducted by public authorities. But the only possible method of dealing with this matter, and in the first place of estimating its importance as immediate or remote, has not been applied. Man can only deal with this difficulty created by his own departure from Nature--to which he can never return--by thoroughly investigating the laws of breeding and heredity, and proceeding to apply a control to human multiplication based upon certain and indisputable knowledge.