THE METABOLIC MACHINERY OF ANIMALS 



299 



We have already traced the changes taking place in the absorbed 

 sugars, chiefly dextrose, and have shown how they may be taken from 

 the blood stream, converted into glycogen, and temporarily stored. 

 Some of this sugar is usually available in the circulating blood which 

 contains 0.1 to 0.15 per cent of it. The muscles likewise store glyco- 

 gen that is used as work is done. Carbon dioxide and water are 

 the final products of carbohydrate oxidation. Experimental evidence 

 indicates that glycogen may be produced from some of the metabolic 



PTOcass: builds protoplasm; 

 . ^lastss. mostly crccttinin 

 and. pifTin. booCies 



by 



deamination 



oarboViydrcLtes 

 formecL by 

 daatninotion 



process : excretion of ^fastes, 



as arao. anct uric acict, 



r'eptilas a.not bircts . 



etirect 

 Combustion 



cLirect 

 combltsCion. 



^ JT 



oCir-ect 

 Combustioa 



process: oxidation, 



Gnergsy relsasscC for~ 

 msto-Dolisra ■ wastes, 

 ■woter ancCearpon dioxide 



/" 



Summary of metabolic processes. 



products of proteins.^ The production of glycogen from fats still 

 lacks conclusive evidence, although there is some indication of indirect 

 conversion. 



The proteins which have been absorbed may be utilized in two 

 ways : (1) in the rebuilding of broken-down protoplasm ; (2) in the 

 supply of energy for work. Consequently, protein substances are 

 often differentiated into tissue builders and energy producers. 



Fats ultimately reach the circulating blood from which they are 

 taken up and used by the various tissues. Fats may be oxidized 

 within the cell to supply energy. In such cases the final products 

 are carbon dioxide and water. When excess fat is eaten it is held in 



1 Howell, Textbook on Physiology, 12th ed. Saunders, p. 869. 



