CHAPTER XX 

 METABOLISM 



It will be recalled that each cell in the body in the living state is the seat 

 of a series of chemic changes which vary in degree from moment to moment 

 in accordance with the degree of functional activity, and on the continuance 

 of which all life phenomena depend. Some of these chemic changes are 

 related to or connected with the molecules of the living material, while 

 others are connected with the food material supplied to them. Of the 

 chemic changes occurring within the molecules some are destructive, dis- 

 similative or disintegrative in character, whereby the molecule is in part 

 eventually reduced through a series of descending chemic stages to simpler 

 compounds which, apparently of no use in the cell, are eliminated from it. 

 It is, therefore, said that the living material undergoes molecular disinte- 

 gration as a result of functional activity. To these changes the term katabol- 

 ism is also applied. Other of these changes are constructive, assimilative or 

 integrative in character, whereby a part at least of the food material furnished 

 by the blood-plasma is transformed through a series of ascending chemic 

 stages into living material, and whereby it is repaired and its former physio- 

 logic condition restored. It is, therefore, said that the living material under- 

 goes molecular integration as a preparation for functional activity. To these 

 changes the term anabolism is also applied. 



Living material has also 'a temperature varying in degree in different 

 species of animals as well as in different parts of the same animal. Here as 

 elsewhere the temperature is due to heat liberated from organic compounds 

 through disruption and subsequent oxidation to simpler compounds. 

 Though some of the heat liberated may come from the tissue molecules, 

 the larger part by far comes from the food molecules sugar, fat, and 

 protein, constituents of the fluids permeating the interstices of the living 

 material. These foods carry into the body potential energy, ultimately 

 derived from the sun. When they are disrupted and oxidized the potential 

 energy is transformed into kinetic energy which manifests itself for the most 

 part as heat. 'To the sum total of all the chemic changes occurring in 

 tissues and foods the term metabolism is given. 



Though the foregoing statements are applied to the individual cell they 

 are equally applicable to the body as a whole, inasmuch as the organs and 

 tissues of which it consists are composed of cells. The body grows in size 

 and maintains its nutrition, by the introduction of food materials which are 

 utilized in part, for the repair of the tissues which have undergone molecular 

 disintegration in consequence of activity, and in part for the liberation of 

 energy. As a result of the disintegration or the metabolism of tissue and 

 food materials, products such as carbon dioxid, urea, etc., are formed which, 

 apparently of no further use, are discharged from the body by eliminating 

 organs as the kidney, lungs, skin, etc. Assimilation and. dissimilation are 

 constantly taking place. If the food assimilated and metabolized exactly 

 replaces the tissues dissimilated and the food metabolized the body will 

 retain a condition of nutritive equilibrium. 



514 



