PHYSIOLOGICAL CHEMISTRY 



PART I 



CHAPTER I 

 INTRODUCTORY 



The scientific field known variously as Physiological, Biologi- 

 cal or Biochemistry is the branch of science which treats of the 

 chemical constitution, reactions and products of living ma- 

 terial, whether of animal or plant origin. There is a growing 

 tendency to use the terms Biological and Biochemistry to de- 

 note the entire field, and to restrict the term Physiological 

 chemistry to that portion of the subject dealing with animal 

 material, but this practice is by no means general. It was once 

 believed that the chemical processes going on in plants and ani- 

 mals were fundamentally different. Synthesis or building up 

 was considered characteristic of plants, whereas animals were 

 known to desynthesize or break down the substances which they 

 ate. We now know that this difference is a quantitative and 

 not a qualitative one, for if kept in the dark, plants take up 

 oxygen, burn their constituents and give off carbon dioxide in 

 a manner analogous to the process predominating in animals. 

 Animals, on the other hand, are now known to be capable of 

 performing numerous and elaborate syntheses, breaking down 

 the materials of their food to simpler compounds, but rebuild- 

 ing many of the fragments into tissue substance, or altering 

 them to produce compounds having specialized biological func- 

 tions. 



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