_Multiplication of the Bacteria._—Marshall Ward and Duclaux have made some special observations in regard to the rapidity with which certain bacteria multiply. Duclaux summarizes the final conclusion thus: taking as a basis the time of 35 minutes for the subdivision into two, which has been frequently observed by Ward, there would be four millions of bacteria produced in twelve hours. The first filaments had plenty of room in a drop culture of one cubic millimeter; but at the end their total volume amounted to the tenth part of the total volume of the drop. At the above rate, making 48 generations in 24 hours, 281,500 billions of organisms would be produced. (Grandeau, Ann. Sci. Agron. Vol. 1, 1905, p. 456). _Aerobic and Anaerobic Bacteria._—As may readily be inferred, the cultural and other surface conditions exert a potent influence both upon the kinds and abundance of the bacteria and molds; since the life-functions of some are dependent upon the presence of free oxygen (“aerobic”), while others flourish best, or only, in the absence of air (“anaerobic”), or are able to avail themselves of the presence of _combined_ oxygen, by reduction of oxids present. Their number is found, in general, to be greatest in cultivated lands, and bacteria are there by far predominant over the moulds. On the other hand, the moulds gain precedence in woodlands and meadows, at least so far as air can gain access; while in the deeper layers of the same, as well as in peaty lands, bacterial life is always scanty. This holds particularly in respect to the nitrifying organisms, and others whose life-functions are dependent upon abundant access of oxygen (aerobic). _Food Material Required._—All bacteria, like the fungi, are dependent for their development upon the presence of adequate amounts of some organic food-material, best apparently in water-soluble form. In the soil it seems to be chiefly compounds of the carbohydrate group, especially various gums derived from the decaying plant substance, or from stable manure; in artificial cultures, glucose is mostly found to be a highly available food. When the decaying substance reaches the state of humus, the latter seems to be available as food only to comparatively few bacteria. The very abundant development of bacterial life seems to be among the most important effects produced by stable manure upon the surface soil, in establishing good tilth (“Bodengare” in German).