HEAT EQUIVALENT OP THE NUTRIENTS OF FOOD/ 



F. Stoiimann, Pii. D., 



IHrector of the A/jriculturalOhemical Institute of the University of Leipsic. 

 INTRODUCTION. 



For the maintenance of life in the broadest sense of the word, the life 

 of i)lants as well as of animals, a regular supply of new material which 

 we call food is necessary. 



This serves in part for the building up of new tissue, in part for 

 rejdacing the tissue lost through metabolism, but most of all in fur- 

 nishing the force or energy which makes life possible, whetlier it mani- 

 fests itself as vital force, heat, or in electrical phenomena. The con- 

 sumption of food is therefore chiefly valuable in giving the body the 

 energy necessary for maintaining life. 



In this last respect there is apparently a fundamental difference 

 between the life of plants and of animals. Although plants can build 

 their tissues from inorganic materials, namely carbon dioxid, water, 

 nitric acid, and certain salts, and although these are regarded as nutri- 

 ents, yet they can give no energy to the plant and, if the energy neces- 

 sary to life must be famished by the food, they can not in the strictest 

 sense be called nutrients. To become such the inorganic substances 

 are changed in the chlorophyll apparatus of the plant into organic 

 compounds laden with energy. This change is effected through the 

 agency of energy in the light and heat of the sun's rays. This is 

 necessary in order to provide the energy Avhich is as necessary for the 

 plant as for the animal. In reality the plant does not live u])on carbon 

 dioxid, water, and the like, but upon organic substances elaborated by 

 the energy of light in peculiar organs which are present in many 

 plants but are lacking in others. The plants Mliich lack these organs 

 are not capable of utilizing the inorganic compounds. In order to 

 build tissue and carry on the functions of a living organism they must 

 feed upon organic, energy-furnishing material. Carbon dioxid, water, 

 and nitric acid are therefore not the food of plants but only the 

 materials from which certain plants can form food. 



» Translated by C. F. Laugwortliy, Ph. D. 

 590 



