32 PHYSIOLOGY OF BACTERIA 



to 0.16 • 10~' mg. of oxygen per cell and hour, in a very poor medium 

 (see p. 188). Figuring on 20,000,000 cells per c.c. as the average 

 during the first three hours of the experiments of Table 7, the 

 amount of oxygen consumed by these cells per hour would be 20 X 

 106 X 0.1 X 10"^ mg. = 2 X 10-^ mg. per c.c, or 2 mg. per liter. 

 Since at 37°, water can dissolve only 6.8 mg. of oxygen, it seems quite 

 probable that in about two to three hours, the oxygen of the medium 

 is all used up, and energy can be produced subsequently only by 

 anaerobic processes which yield much less energy (see p. 27). 



(d) THE NEED FOR ENERGY 



It seems justifiable to question why microorganisms 

 need energy for growth. Yeast cells are made from the 

 malt protein and eventually from sugar, and the com- 

 bustion heat of these foods is about the same as that of 

 the new cells. The same is evident in the examples of 

 Tangl's experiments given in Table 6 p. 28. 



Since the cells are not built directly from the peptone 

 or protein, these materials must be first reduced to much 

 smaller units, amino-acids or, sometimes, even smaller 

 molecules. The architecture of yeast protoplasm is 

 quite different from that of barley protoplasm, and the 

 architecture of protoplasm of B. anthracis is widely 

 different from that of a commercial peptone. The 

 breaking down will produce some energy, but this small 

 amount is not nearly sufficient to weld the small particles 

 into the new structure. Extra energy must be added 

 to bring about new construction. This accounts for 

 some of the energy wasted by bacteria, as well as by all 

 other organisms. However, it does not account for all 

 the waste. 



gi After growth has ceased, the cells continue for a 

 considerable period to liberate energy. Meyerhof (1914) 

 has shown that life, as such, is not based upon a higher 

 potential energy in the living cells. He killed a thick 



