only under high powers of the microscope and which reproduce their kind with astonishing rapidity, gaining access to the surface or interior of the body, begin there to thrive and multiply, taking up from the living animal material for their own nourishment, thus robbing their host of that upon which his tissues must live, while at the same time, as the result of their activity, they produce{322} various substances which, so far as they are concerned, are excretory in nature, and many of which are extremely poisonous to the animal organism which harbors them. Such a disease as puerperal fever, for instance, is simply an expression of the fact that within the living human body there is going on active putrefactive action by which the internal cells are being destroyed. this destruction being progressive and often far-reaching; and that, as the result of their presence in the still living body, the noxious or toxic excretory materials of which they get rid are absorbed, in consequence of which such varying symptoms as nausea, fever, purging, vomiting, delirium, and many other symptoms are produced, the objective evidence of their local activity being the actual destruction of tissues, as is seen in cases of abscess, phlegmonous erysipelas, etc. The condition known everywhere as gangrene, when moist and offensive, is nothing but the putrefaction of tissues _en masse_ which are not yet detached or separated from the living body of which they but recently formed a living part. Experiments with organic material outside the body have amply demonstrated that such putrefactive processes can be checked by certain precautions--such as filtration of air, heat, etc. It remained for the genius of Lister to show how similar processes of putrefaction and exclusion of germs could be made serviceable for the prevention of disease in the human race. To Lister, then, is due the credit of having originated the antiseptic system and brought about a condition long yearned for by surgeons throughout the world, but never previously attained. What a revolution he wrought by his masterly researches can be appreciated only when one compares the impunity with which surgeons now perform operations which, in the previous era were regarded as absolutley unjustifiable--a conclusion amply warranted by the statistics of that era. Great as the credit due to Lister, it is equally desirable to state that his work was, for the most part, based upon Lister's, the{323} researches of Tyndall, Pasteur, and Koch, which had established the germ nature of the terrible infectious diseases and the germicidal effect of filtration, of heat, and of certain other substances and methods which permitted of the development of his own system. [Illustration: 0343]