INTKODUCTION. xliii 



C. 51-5-54-5 1 

 H. 6-9- 73 I 



The proteids contain per cent.: -j K 15-2-17-0 i ( 248 and 249). 



O. 20-9-23-5 | 

 S. 0-3- 2-0 J 



A man who takes a certain amount of this food adds thereto oxygen from the 

 air in the process of respiration. Combustion or oxidation then takes place, where- 

 by chemically-potential energy is transformed into heat. 



It is evident that the products of this combustion must be bodies of simpler con- 

 stitution bodies with less complex arrangement of their atoms, with the greatest 

 possible saturation of the affinities of their atoms, of greater stability, partly rich in 

 O, and possessing either no potential energy, or only very little. These bodies are 

 carbon dioxide, C0 2 ; water, H 2 ; and as the chief representative of the nitro- 

 genous excreta, urea (CO(NH 2 ) 2 ), which has still a small amount of potential 

 energy, but which outside the body readily splits into C0 2 and ammonia (NH 3 ). 



The human body is an organism in which, by the phenomena of oxidation, the 

 complex nutritive materials of the vegetable kingdom, which are highly charged 

 with potential energy, are transformed into simple chemical bodies, whereby the 

 potential energy is transformed into the equivalent amount of kinetic energy (heat, 

 work, electrical phenomena). 



But how do plants form these complex food-stuffs so rich in potential energy ? 

 It is plain that the potential energy of plants must be obtained from some other 

 form of energy. This potential energy is supplied to plants by the rays of the 

 sun, whose chemical light-rays are absorbed by plants. Without the rays of the 

 sun there could be no plants. Plants absorb from the air and the soil C0 2 , H 2 0, 

 NH 3 , and N, of which carbon dioxide, water, and ammonia (from urea) are also 

 produced by the excreta of animals. Plants absorb the kinetic energy of light from 

 tlie suris rays and transform it into potential energy, which is accumulated during 

 the growth of the plant in its tissues, and in the food-stuffs produced in them 

 during their growth. This formation of complex chemical compounds is accom- 

 panied by the simultaneous excretion of O. 



Occasionally, kinetic energy, such as we universally meet with in animals, is liberated in 

 plants. Many plants develop considerable quantities of heat in their flowers, e.g., the arum 

 tribe. We must also remember that during the formation of the solid parts of plants, when 

 fluid juices are changed into solid masses, heat is set free. In plants, under certain circum- 

 stances, O is absorbed, and C0 2 is excreted, but these processes are so trivial as compared with 

 the typical condition in the vegetable kingdom, that they may be regarded as of small 

 moment. 



Plants, therefore, are organisms which, by a reduction process, transform simple 

 stable combinations into complex compounds, whereby potential solar energy is 

 transformed into the chemically-potential energy of vegetable tissues. Animals 

 are living beings, which by oxidation decompose or break up the complex grouping 

 of atoms manufactured by plants, whereby potential is transformed into kinetic 

 energy. Thus, there is a constant circulation of matter and a constant exchange of 

 energy between plants and animals. All the energy of animals is derived from 

 plants. All the energy of plants arises from the sun. Thus the sun is the cause, 

 the original source of all energy in the organism, i.e., of the whole of life. 



