GENERAL FOOD RELATIONSHIPS— METABOLISM 81 



The material diffuses into the cell over its entire surface 

 with little hindrance. The bacteria are usually distributed 

 throughout the medium, so that there is very intimate con- 

 tact in all parts of the mass which favors rapid chemical 

 action. The following calculation illustrates this: 



The volume of a coccus Ip in diameter is 0.5236 x 10"i* c.c. 

 The surface of a coccus l;u in diameter is x x 10-* sq. cm. 



It is not uncommon to find in milk on the point of sour- 

 ing 1,000,000,000 bacteria per c.c. 



Assuming these to be cocci of 1/i diameter the volume of 

 these bacteria in a liter is only 0.05 c.c. or in the liter there 

 would be 19999 parts of milk and only 1 part bacteria. "The 

 surface area of these bacteria is 3141.6 sq. cm. With this 

 large surface exposed, it is not strange that the change from 

 "on the point of souring" to "sour" occurs within an hour 

 or less. 



Although large numbers of bacteria can and do cause 

 great chemical changes the amount of material actually 

 utilized for maintenance of the cell is very slight, infinites- 

 imal almost, and yet is fairly comparable to that required 

 for man, as is illustrated by the following computations: 



E. Kohn has shown that certain water bacteria grew well 

 in water to which there was added per liter 0.000002 mg. 

 dextrose, 0.00000007 mg. (NH4)2S04 and 0.0000000007 mg. 

 (NH4)2HP04. The bacteria numbered about 1000 per c.c. 

 Taking the specific gravity at 1 (a little too low) the mass 

 of the bacteria in the liter was about 0.001 mg. Hence the 

 bacteria used 0.002 of their weight of carbohydrate and 

 0.00007 of ammonium sulphate. A 150-pound (75-kilo) man 

 can live on 375 g. of sugar (0.005 of his weight) and 52.5 g. of 

 protein (0.0007 of his weight). 



