CHEMICAL COMPOSITION OF THE HUMAN BODY 13 



4. Nine-tenths of the oxygen appears in the form of water; in 

 small proportions it is present in carbonic, sulphuric, and phos- 

 phoric acids and their salts. Besides this, it is present in all organic 

 compounds of the body (except in a few hydrocarbons in the 

 intestine). 



5. A small part of the sulphur is present in the sulphates; 

 another, still smaller portion, in the sulphuretted hydrogen and 

 iron sulphide (intestine); by far the largest part is found in the 

 proteids, where it appears in two forms, as reduced (easily split off 

 by boiling with alkali) and as oxidized (strongly united with the 

 proteid molecule). It seems to be present in bcth forms in the 

 metabolic products of the proteids. 



6. Phosphorus seems to be present in inorganic and organic 

 compounds only in the form of phosphoric acid which forms salts 

 with alkalies and calcium, the calcium salt forming a chief con- 

 stituent of the skeleton. Organic compounds containing phos- 

 phorus are lecithin, jecorin, protagon, nuclein. 



7. Iron, deposited as inorganic, i.e. in a form demonstrable by 

 the ordinary reactions, in the liver and spleen (probably as oxide), 

 is found also in the contents of the intestine (as iron sulphide). 

 Of special physiological interest are the organic iron compounds, 

 the most important of which is haemoglobin, the red coloring 

 matter of blood. Many nucleo-albumins also contain a little iron. 

 The organic compounds of iron which do not give the general iron 

 reactions are called metal -organic compounds. 



The elements thus far described are the most important as they 

 are the organogenic elements, so termed because they form the 

 organic substances of the body. 



The other four elements which are united with organic sub- 

 stances, especially proteid substances, do not appear in metal- 

 organic compounds, hence it is concluded that these elements are 

 present in the organism only in the form of salts or inorganic com- 

 pounds. 



8 and 9. Potassium and sodium, in about equal proportions, 

 uniting chiefly with carbonic, hydrochloric, and phosphoric acids, 

 form acid and neutral salts. Potassium salts predominate in the 

 tissue-cells, sodium salts in the tissue-fluids. The alkali-metals 

 also form salt-like bodies with the proteids. 



10 and ii. Calcium and magnesium, as the salts of carbonic 

 and phosphoric acids, form the chief constituents of the bones. 

 Calcium, either alone or with phosphoric acid, is also united with 

 proteids. 



12. Chlorine is present as free hydrochloric acid (in gastric 

 juice); or united with an alkali, especially sodium, predominates 

 in the tissue fluids. In gastric digestion, hydrochloric acid forms 

 acid hvdrochlorates with the products of proteid digestion. 



