Page:Popular Science Monthly Volume 6.djvu/418

402 carried even below zero, and yet the movements will recommence as soon as it is raised again above 40° or 45°. Exposure to a temperature of 140° will kill them; but this result seems to depend quite as much upon the length of time during which they are exposed to it, as upon the degree of heat itself, several hours being required for the lesser degrees, while ten to fifteen minutes, at boiling heat, are sufficient, and even four or five at 215°.



In the air, bacteria, or bacteria-spores, exist, but only in moderate numbers, for exposure to the air often fails to cause cloudiness of artificial nutritive liquids, when the plants that existed in them before-hand have been destroyed by heat; and sometimes portions of meat taken from a recently-killed animal, with all possible precautions to prevent inoculation with bacteria through the instruments employed, and placed in open vases that have been washed in alcohol and then scorched in a hot flame, remain for days and weeks without putrefying. They are present in all kinds of water, and generally in considerable numbers. Cohn found them in the vapor condensed upon the inner surface of a bell-glass placed over a dish of water; and it is probable that those found in the air are enabled to live by the moisture contained in it. Their presence in the liquids and tissues of the body, often affirmed and denied, is now proved beyond question, Billroth's experiments on this point having been repeated and confirmed very recently by Tiegel. Rapid multiplication in the living body is prevented in part by the motion of the blood, and in part by the vital energy of the tissues, which is so vigorous that these plants cannot check it, and thereby obtain the nourishment needed for their own growth; but, when life has ceased, or when an abnormal condition of the tissues has been brought about by any cause, then rapid growth begins, and we have, in the one case, putrefaction; in the other, various pathological changes of more or less importance.

About the year 1865, two physicians of Strasburg, Messrs. Coze and Feltz, published a series of experiments which they had made with inoculations of putrid matter; and in 1872 they published a book upon the same subject, claiming that the virulent effects of putrid matter were due to the presence and growth of bacteria, and that the blood of an animal poisoned with such matter was itself virulent to a