[Illustration: PASTEUR IN HIS LABORATORY. _facing p. 44._] Now--and I appeal to the good sense of my readers--would it be better to efface the suffering of those rats, those guinea-pigs, those rabbits, and return to the olden times when the mortality in lying-in hospitals was often 40 per cent. (it is to-day, 0.02 per cent.!)? Must we condemn Lister and Pasteur as great criminals because they dared to inoculate microbes into a few rabbits and bring about in those unfortunate animals--they would have died a long time ago even without that--experimental ailments in order to ward off malignant diseases from thousands and thousands of human beings? * * * * * The second discovery which I shall mention is that of the infectiousness of tuberculosis. Thousands and thousands of doctors had had tuberculous patients under their care. Three thousand years ago, Hippocrates described tuberculosis with as much precision as could be done to-day. Illustrious physicians in every land had tried to analyse the nature of this terrible disease and to unravel its cause; nevertheless, they were unable, from clinical observation alone, to prove what is to-day quite commonplace knowledge, viz., that tuberculosis is infectious. In 1864, a French doctor, Villemin, conceived the simple and ingenious idea of inoculating rabbits with the tuberculous matter found in the lungs of consumptive patients. These rabbits became tuberculous; they died in a few weeks with tuberculous granulations in lungs and liver. It was thus demonstrated that tuberculosis was infectious. Later on, in 1878, Koch discovered that the active agent of this infection is a special microbe. But, however important may be the discovery of the microbe of tuberculosis (the tubercle-bacillus of Koch), the essential dominating fact is that tuberculosis is infectious. As soon as this great fact became known, a profound revolution occurred in social hygiene, in the treatment and in the prevention of this terrible evil. We know now the consumptive man carries in his lungs and sputum the germ capable of developing the same evil in others; consequently we know how to preserve ourselves against tuberculosis. We must purify or destroy the habitations wherein consumptives have lived, burn or carbolise all the sputum, make spitting in public places a punishable offence, take sanitary measures against unhealthy meat, defend our children against contaminated milk--in a word, we are armed against a disease, the sole and unique cause of which, as experimentation alone has taught us, is infection.