CHAPTER III. 

 THE CHEMICAL COMPOSITION OF THE BODY. 



OF the eighty chemical elements which have been isolated, no less than 

 seventeen combine in varying quantities to form the chemical basis of the 

 animal body. The substances which contribute the largest share are the 

 non- metallic elements, Nitrogen, Oxygen, Carbon, and Hydrogen oxygen 

 and carbon making up altogether about 85 per cent, of the whole. The 

 most abundant of the metallic elements are Calcium, Sodium, and Potassium.* 



These elements do not exist in the animal body in the free state, but are 

 combined into complex chemical compounds. 



The first step in the act of separating the composition products of proto- 

 plasm produces changes which destroy the chemical and physical relations 

 of these products which maintain the state of life. Dead protoplasm, how- 

 ever, yields a number of substances which must be very directly derived 

 from the living protoplasm. On the other hand, certain products can be 

 isolated from the animal body w r hich are evidently not a part of the proto- 

 plasm itself, but products of protoplasmic activity. Some of these, like fat, 

 glycogen, etc., are constructive products, others are disintegration products 

 of protoplasmic activity. 



THE NITROGENOUS SUBSTANCES. 



The nitrogenous substances in the body consist chiefly of the proteins 

 or of substances which are derived from the proteins. Nitrogenous sub- 

 stances occur in the solid tissues of the body and are found also to a con- 

 siderable extent in the circulating fluids (the blood and lymph) and in the 

 secretions and excretions. 



* The following table represents the relative proportion of the various elements in 

 the body. (Marshall.) 



Oxygen 72.0 



Carbon 13 . 5 



Hydrogen 9.1 



Nitrogen 2.5 



Calcium 1.3 



Phosphorus * J 5 



Sulphur o. 1476 



Sodium o.i 



Chlorine 0.085 



79 



Fluorine o. 08 



Potassium o . 026 



Iron o.oi 



Magnesium 0.012 



Silicon o. 0002 



(Traces of copper, lead, and alu- 

 minum) 



100 



