Like all living organisms, bacteria propagate themselves. The most usual method is by fission or by partition, though Magnin and Cohn have recorded their observations on the formation of spores and sporangia, and I have myself witnessed the last named method. It is of importance to note that while the bacterium is killed by continued exposure to temperatures of freezing or 176° F., the spores will germinate after protracted exposure to temperature as high as 205° F. or as low as °123 F. These spores will also withstand complete desiccation, and it is in this form, mixed with the air we breathe and move in, that present the conditions from which all zymotic diseases originate. Miguel has shown that, while the air contains very few adult bacteria, it contains myriads of their spores. To the researches of Koch, Pasteur, and others, we are indebted for the certain information that, while these omnipresent germs withstand such vicissitudes of temperature, they require certain food for their maintenance; and though we cannot as yet tell what that food is, we know that when nutrient material is submitted to their action they thrive for a time, and when the particular principle which supports them is exhausted they die. This is particularly true of pathogenic germs, and the accepted theory of the bacillus tuberculosis, or the germ of consumption, is a good illustration. It has been demonstrated by Koch, Klein, Pasteur, Frankell, Sternberg, and others, that they require some product of inflammatory action for their support within the body of their victim. This is also true of cholera, at least so far as their dietary requirements are concerned. The animal cannot be infected with tuberculosis by merely introducing the germ-laden material into the stomach or upon any of the mucous membranes; but if an inflammatory condition be present, either due to the puncture of the introducing needle or scalpel, or to extraneous causes, such as a catarrhal condition of the lungs, tuberculosis is as sure to follow as the sun is to rise again.