ORGANIC STRUCTURE: CHEMICAL 21 



7. ON THE ULTIMATE CHEMICAL STRUCTURE OF 



ORGANISMS 



ya. The Ultimate Chemistry of Inorganic Things. A 

 small part of the earth is known directly — this part includes 

 the rocky crust to a few miles deep ; the watery envelope, or 

 ocean, and the gaseous envelope, or atmosphere. The deep 

 interior of the earth is indirectly known. 



The outer envelopes of the sun and the stars and the materials 

 of some nebulae are directly known in that it is possible to deduce 

 the chemical materials from the nature of the emitted light- 

 radiation. The chemical structure of some meteoritic bodies 

 is directly known. 



It is possible to infer the chemical structure of those parts of 

 the universe that are not directly accessible to observation. With 

 such reservations it may be stated that the ordinary matter of 

 the universe is constituted by about 100 different kinds of chemic- 

 ally elementary substances. 



The crust of the solid earth. The most frequently occurring 

 chemical elements and their percentages of the earth's crust are 

 oxygen 50 per cent., silicon 26, aluminium 7, iron 4, calcium 3, 

 magnesium 2, sodium 2, potassium 2, hydrogen i, titanium 0-5, 

 carbon 0-18, chlorine 0-2, bromine 0-2, phosphorus o-ii, sulphur 

 o-ii, barium o-o8, manganese o-oS, strontium 0-02, nitrogen 0-03, 

 fluorine o-i, all other elements 0-5 per cent. Thus about 90 

 per cent, of the directly known materials of the solid crust of the 

 earth consists of the five elements oxygen, silicon, aluminium, 

 iron and calcium. 



The watery envelope. This consists of oxygen and hydrogen, 

 in the form of water, and contains, in solution, about 3-5 per cent, 

 of other elements, mainly sodium and chlorine. There are 

 measurable, or unmeasurable, minute quantities (say per 10 

 litres) of nearly all the other known elements. 



The gaseous envelope. This consists of about 79 per cent, of 

 nitrogen, 20 per cent, of oxygen, water vapour, carbon dioxide, 

 oxides of nitrogen, argon, helium, hydrogen, etc. 



yb. The Ultimate Chemistry of Organisms. There are 

 very few complete analyses of the bodies of animals or plants. 

 The following, however, is the ultimate composition of the body 

 of a man : 



