2 20 PHYSIOLOGY OF NUTRITION 



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

 section, p. 218.) 



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 necessitv 

 in every active cell. 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. 1 



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 C0 2 used for a gram-molecule of carbohydrate (employing the 

 empirical formula for starch, C 6 H 10 O 5 ) is 97,600 X 6, or 585, 600 g.-cal.' Experi- 

 ment shows that the heat of formation of a gram-molecule of carbohydrate 

 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 H 2 0. 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 5 molecules 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 produces an apparent excess of heat above that which is calculated 

 from the amount of carbon dioxide eliminated, 2 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 observation (667,000). The differences encountered in Bonnier's experi- 

 ments 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 liberated without the occurrence of oxidation . 



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



CO 



heat production occurs when the respiratory ratio, —=. , assumes a minimum 



U2 



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 



1 Ostwald, Wilhelm, Theoretische Chemie. Moscow, 1891. P. 73.* 



2 Ostwald, Wilhelm, 1801.* [See reference just given.] 



1 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 5 molecules of water. In other words, C 6 Hio0 5 is considered as though it were 6C + 5H0O. 

 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 C 6 Hi O 5 from 6C + 5H0O 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. 



