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, Oxygen, Carbon, Hydrogen, and Nitrogen 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. Of course we cannot analyze 

 the living protoplasm and isolate its 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 which 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. 



A large number of the animal compounds, particularly those of the nitrog- 

 enous group, are characterized by their complexity. Many elements enter 

 into their composition, and many atoms of the same element occur in each 

 molecule. This latter fact no doubt explains the reason of their instability. 



Of the numerous compounds that have been isolated from the animal 

 body, only a very few of the most important will be discussed in this chapter. 



* 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 i .3 



Phosphorus 1.15 



Sulphur 0.1476 



Sodium o.i 



Chlorine 0.085 



78 



Fluorine 0.08 



Potassium 0.026 



Iron o.oi 



Magnesium 0.0012 



Silicon 0.0002 



(Traces of copper, lead, and alu- 

 minum) 



