4 o2 THE POPULAR SCIENCE MONTHLY. 



carried eveu below zero, and yet the movements will recommence as 

 soon as it is raised again above 40 or 45. Exposure to a tempera- 

 ture 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 suf- 

 ficient, and even four or five at 215. 



Fig. 3. Bacteria, Leptothrix, and Spore-like Bodies found in a Solution of Ammonic 

 Carbonate and Sodic Phosphate. The tuft at the end of the filament of Leptothrix is 

 probably an accidental accumulation of fragments. 



In the air, bacteria, or bacteria-spores, exist, but only in moderate 

 numbers, for exposure to the air often fails to cause cloudiness of arti- 

 ficial 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 con- 

 tained 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 pre- 

 vented 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 18*72 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 



