200 PHYSIOLOGY OF NUTRITION 



and other hydrolytic processes. (See last paragraph of the next preceding 

 section, p. 198.) 



More mature, growing stems are seen to be different from germinating seeds 

 in this regard; while the calculation leads us to expect a rate of heat production 

 here of 3 g.-cal. per minute, the calorimetric determination shows that no heat 

 is liberated at all. In this case the energy is not set free as heat but must be con- 

 sidered as taking the form of work, the accomplishment of which is a necessity 

 in every active ceU. Work and heat are merely different modifications of the 

 same thing, energy — just as the yellow and red varieties of phosphorus, or the 

 diamond and amorphous carbon, are simply different forms of matter. ' 



Some thermo-chemical considerations are of interest in this connection. 

 The heat of formation of carbon dioxide is 97,600 g.-cal. per gram-molecule, 

 and that of the formation of carbohydrate (employing the empirical formula 

 for starch, CeHioOs) is 97,600 X 6, or 585,600 g.-cal.' Experiment shows this 

 to be actually 667,000 g.-cal., however, and the excess (81,400 g.-cal., the so- 

 called heat effect) is the amount of heat corresponding to the formation of a 

 gram-molecule of starch from C and H2O. The heat of combustion of starch is 

 thus made up of the heat of formation of 6 molecules of carbon dioxide and that 

 of the combination of water with these. When carbohydrates are completely 

 oxidized in the animal body there is the same excess of heat (81,400 g.-cal.) 

 above that of the oxidation of the carbon in the carbohydrate molecule. This 

 explains the fact — not otherwise to be understood — that the animal body pro- 

 duces an apparent excess of heat above that which is calculated from the amount 

 of carbon dioxide eliminated,^ or from the quantity of oxygen absorbed, this 

 calculation being based simply on the oxidation of carbon to carbon dioxide. 

 In the concrete case just considered, the calculated heat of combustion of 

 starch (585,600) is about six-sevenths of the value obtained by direct observa- ' 

 tion (667,000). The differences encountered in Bonnier's experiments are so 

 great, however (see the table given above), that they are not to be referred 

 simply to the heat effect. It is strongly suggested that reactions occur in seed 

 germination whereby heat is hberated without the occurrence of -oxidation. 



The experiment of Bonnier above described shows that the highest rate of 



heat production occurs when the respiratory ratio, -p— ^ assumes a minimum 

 value and the rate of oxygen absorption is much accelerated. 



§8. Anaerobic, or Intramolecular Respiration.— When plants that usually 

 require oxygen are placed in an oxygen-free atmosphere they do not die at once 



■ Ostwaia, Wilhelm, Theoretische Chemie. Moscow, 1891. P. 73.* 

 " Ostwald, Wilhelm, 1891.* [See reference just given.) 



' This number corresponds to the formation of 6 gram-molecules of carbon dioxide from 

 carbon and oxygen, the hydrogen and oxygen of the starch molecule being considered simply 

 as 6 molecules of water. In other words, CeHioOs is considered as though it were 6C + sHjO. 

 The hydrogen and oxygen of starch are not combined to form water, however, and, as is brought 

 out in the next sentence of the text, the heat of formation of CoHioOs from 6C + sHaO is the 

 excess there referred to. The German edition agrees with the 7th Russian edition in stating 

 this excess as 82,300, instead of 81,400 g.-cal. — Ed. 



