PHYSIOLOGICAL CHEMISTRY. 



CHAPTER I. 



INTRODUCTION. 



THE science of physiological chemistry has for its object the 

 study of the various chemical processes which take place in the 

 bodies of animals and plants, and which are more or less intimately 

 associated with the phenomena of life. As the phenomena of life, 

 moreover, are essentially dependent upon the transformation of 

 living matter into non-living matter, and vice versa, physiological 

 chemistry deals primarily with the chemical processes of nutrition 

 in the widest sense of the term. Its study therefore comprises a 

 consideration of the various substances which are generally desig- 

 nated as food-stuifs, their origin, their transformation into living 

 tissue, and their ultimate fate. 



General Composition of Living Matter. Chemical examina- 

 tion shows that plants and animals consist essentially of carbon, 

 hydrogen, nitrogen, oxygen, sulphur, phosphorus, chlorine, potas- 

 sium, sodium, calcium, magnesium, and iron that is, of elements 

 which occur also widely distributed in the non-organized world. 

 In the bodies of animals and plants these elements are built up to 

 form bodies of highly complex chemical constitution, which belong 

 to the class of albumins, carbohydrates, and fats. Upon their pres- 

 ence both animals and plants are dependent for their existence, and 

 as these bodies are constantly being broken down and transformed 

 into simpler chemical compounds, as the result of the various mani- 

 festations of life, it follows, from the law of the indestructibility 

 of matter, that for their replacement the living body is forced to 

 depend upon such simpler matter as is pre-existent. This matter 

 it is capable of transforming into the complex substances of which 

 its tissues are composed. 



Forces at Work in the Living World. The forces which are 

 at work in effecting these various changes are the same as those 

 which we meet with in the non-organized world. They represent 

 essentially a transformation of energy, of which, as we shall presently 

 see, the sunlight is the ultimate source. It would thus appear that 

 life in itself is solely a physical phenomenon, and that its various 



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