GROWTH 181 



protoplasm is quite different from that of the peptone 

 molecule, and that the peptone molecule has to be torn 

 into very small units before it can be used in the con- 

 struction of protoplasm. The tearing down will yield 

 energy which may not be available, and the building up 

 will require energy. The combustion heat of the proto- 

 plasm tells only how much energy is contained, and not 

 how much energy was necessary to construct it. Growth 

 processes do not work with 100% efficiency as we shall 

 see later. 



The other error is made by the assumption that the 

 combustion heat (or the balance of combustion heats 

 in anaerobic fermentations), represents available energy. 

 According to thermodynamic laws, the ^'free energy," 

 i.e., the energy that might be used to do work, is not 

 identical with the combustion heat, or differences of 

 these. These values represent the total energy Hberated 

 by the fermentation, but part of this goes towards 

 the increase of entropy, and is lost for any work. This 

 amount varies greatly with the kind of process. 



Let the combustion of glucose serve as example (Baas-Becking and 

 Parks, 1927) 



CeHisOe + 6 O2 = 6 CO2 + 6 HoO 



Solid Gas Gas Liquid 



Under the above conditions (solid sugar; oxygen and CO 2 at 

 pressures of 1 atm.; water of combustion in liquid form), we have 



Calories 



Heat of combustion ^ 685,800 



Free energy 674,000 



Entropy increase 11,800 



The heat going towards the increase of entropy which cannot be used 

 for any work, is 1.7 % of the combustion heat. A mold oxidizing one 



