64 FOOD REQUIREMENTS 



in the water, they obtain some food from volatile compounds of 

 the air, like carbon monoxid (CO), carbon dioxid (CO 2 ), ammonia 

 (NH 3 ), hydrogen (H) and perhaps methane (CH 4 ). Under all 

 circumstances the amount of food used is very small." 



Maximum Requirements. The maximum quantity of food which 

 may be decomposed by bacteria is often enormous. They quickly 

 decompose the body of an ox after its death. Tons of material 

 run into the septic tanks of large cities, all of which is rapidly 

 decomposed by bacteria. It is, however, usually the case that the 

 speed of the reaction is great at first, but soon slows up or comes 

 to a complete stop. This is due to the fact that the accumulation 

 of end-products interferes with the growth of bacteria. This is 

 true in milk where at first the lactose is rapidly changed to lactic 

 acid, which if not neutralized soon becomes concentrated enough, 

 to slow up the reaction. This is also true with the changes going 

 on in sauerkraut and silage. 



Function of the Food. The food utilized by bacteria has two 

 functions, namely, the furnishing of energy and the acting as cellular 

 building material. The quantity required by each bacterial cell 

 for building material is not great, for MacNeal and his associates 

 found that the dry matter of 550,000,000 cells of B. coli weigh 

 only 0.1 mg. Others have estimated the weight of a single colon 

 bacillus to be 0.000,000,163 mg., or it would require 1,600,000,000 

 colon bacilli to weight approximately 1 mg. The waste products 

 and repair material would make the cellular requirements slightly 

 greater than this, but from these figures it is evident that the actual 

 quantity required by a cell for building material is extremely small. 

 Even this, however, is not immaterial, for Conn starting with the 

 assumption that the period of generation is a half hour makes the 

 following calculation. "If we take a single bacillus measuring 

 2 M in length and 1 M in breadth, with a weight of 0.000,000,001,571 

 mg., it will increase, according to the aforesaid assumption, at 

 such a rate that in two days' time its progeny will amount to 

 281,000,000,000, and will occupy a volume equal to about ^ liter 

 (30.51 cu. in.); within a further three days the quantity would 

 increase to a mass sufficient completely to fill the beds of all the 

 oceans of the globe." Due to the accumulation of waste products 

 they never continue to multiply long at such a rate, but the numbers 

 in suitable media often become hundreds of millions per cubic 

 centimeter before retardation occurs. 



Source of Energy. Animals and plants require energy in their 

 life activity, the former obtaining it directly from the kinetic 

 energy of the sun which they store up as potential energy. 

 This is liberated by the animal in the process of oxidation. Now, 

 bacteria do not possess the powers of the higher plants to utilize 

 directly the energy of the sun, but, like the Animals they are 



