686 Journal of Agricultural Research voi. xii. No. n 



the heat was produced by chemical or microbial causes. Gore {191 1, 

 P- 33) concluded that in self-heating, physiological processes are probably 

 the first to operate. Oxidizing enzyms are the active agents in many 

 cases. Chemical oxidation would intervene only when the temperature 

 had been raised to the combustion point of the substances present. Gore 

 presents formulas and graphs illustrating the theoretical progress of the 

 accumulation of heat. 



The studies of E. M. Bailey {1912) on the ripening of bananas indicate 

 that bacterial activity is not responsible for the heat produced or other 

 changes resulting during the ripening of the fruit. 



Nabokich {1903) found that seeds which had been sterilized by chemi- 

 cals such as mercuric chlorid respired during the first few days as much 

 carbon dioxid as did the controls. In some instances the respiration 

 of the sterilized seeds exceeds that of the controls. 



Respiration may be briefly defined as the release of energy through 

 the biochemical oxidation of organic compounds as accelerated by certain 

 enzyms. Carbon dioxid and water are the characteristic chemical end 

 products. It is shown by De Saussure {1804) that respiration was ac- 

 companied by the disappearance of oxygen. Pfliiger {1875) maintained 

 that the inspired oxygen combines in some manner with cyanogen radi- 

 cals of the living protoplasm. This effects a readjustment, as the result 

 of which carbon dioxid and water are eliminated. The decomposition 

 is of an explosive character, and the reaction liberates heat energy. 



Verworn {1899, p. 483) evolved the " biogen" theory, according to which 

 the oxygen enters the "biogen molecules," which are thus rendered less 

 stable. Slight impulses are then required to bring about a chemical 

 union of this oxygen with the carbon in the cyanogen group. 



Since the grain itself is a poor conductor of heat, it follows that the heat 

 energy released through respiration accumulates in the mass in propor- 

 tion to its bulk so that the increase in temperature may in time become 

 very marked. 



MATERIAL OXIDIZED IN RESPIRATION 



In the case of resting tissues and storage structures, such as the grain 

 kernel or caryopsis, the exact character of the substrate or material 

 oxidized in respiration is of significance. Wehmer {1892) fed Aspergillus 

 on peptone, and found it capable of satisfying its requirements from 

 this source. Gore (19 14) found that in ripening bananas the rate of 

 starch hydrolysis paralleled the rate of respiration. There was slight 

 change in the quantity of protein and fats in the fruit. Maige and 

 Nicolas {1910) found that the immersion of etiolated leaves, shoots, or 

 seedlings in sugar solutions resulted in an increased rate of respiration. 



Langworthy and Milner (1913) observed that in ripening bananas the 

 "thermal quotient," or quantity of heat produced per unit of carbon 

 dioxid respired, indicated the combustion of carbohydrate. The thermal 



