INTRODUCTION 19 



study of the chemistry of protoplasm, its products and the sub- 

 stances which it requires for the continuance of its normal 

 functions. 



Material Bases. Amounts in Body. In beginning the study 

 of so broad and complicated a field it is difficult to choose a 

 point of attack. The most satisfactory plan will be first to be- 

 come familiar with the chemical substances out of which living 

 material is made up. The number of these compounds is nat- 

 urally large, but for convenience they may be classified in five 

 great groups which are given the name of the Base Materials, 

 or Material Bases. 



The five groups are as follows : 



i. Inorganic materials including water. 



n. Carbohydrates. 



m. Fats, Phosphatids and related compounds, 

 iv. Proteins. 



v. Extractives. 



Our first task will be to become familiar with the character- 

 istics and properties of the Material Bases, studying group 

 reactions and also the specific properties of important individ- 

 ual compounds, and methods for their detection and estima- 

 tion. We will then trace the history of the various substances 

 in their passage through the body, considering their fate in 

 the alimentary canal, their subsequent behavior as constitu- 

 ents in the body tissues and fluids, and the final elimination of 

 end products formed by their destruction. 



The relative amounts of the different classes of Material 

 Bases in the animal body are somewhat variable. Water and 

 other inorganic materials make up about 65-70% of the entire 

 body weight of which only 4.5-5% is ash and the remainder 

 water. Carbohydrates are present only in small quantities, the 

 amount being less than 1%. Fats and related compounds vary 

 considerably in amount with the general state of the body, 

 since they may be stored away in large quantities. The body 

 contains on the average about 15%. Proteins vary less from 



