8 THE MECHANISM OF LIFE 



with minerals, metalloids, and metals. We now know that a 

 living organism is composed of exactly the same elements 

 as those which constitute the mineral world. These are 

 carbon, oxygen, hydrogen, nitrogen, phosphorus, calcium, iron, 

 sulphur, chlorine, sodium, potassium, and one or two other 

 elements in smaller quantity. It was formerly supposed that 

 the organic combinations of these elements were found only 

 in living organisms and could be fashioned only by vital 

 forces. In more recent times, howevei - , an ever increasing 

 number of organic substances have been produced in the 

 laboratory. 



Organic bodies may be divided into four principal groups. 



(1) Carbohydrates, including the sugars and the starches, all 

 of which may be considered as formed of carbon and water. 



(2) Fats, which may be considered chemically as the ethers of 

 glycerine, combinations of one molecule of glycerine and 

 three molecules of a fatty acid, with elimination of water. 



(3) Albuminoids, substances whose molecules are complex, con- 

 taining nitrogen and sulphur in addition to carbon, oxygen, 

 and hydrogen. The albuminoid of the cell nucleus also 

 contains phosphorus, and the haemoglobin of the blood 

 contains iron. (4) Mineral* or inorganic elements, such as 

 chloride of sodium, phosphate of calcium, and carbonic acid. 

 This group also includes water, which is the most important 

 constituent, since it forms more than a moiety of the sub- 

 stance of all living creatures. 



Wohler in LSy.8 accomplished the first synthesis of an 

 organic substance, urea, one of the products of the decom- 

 position of albumin. Since then a large number of organic 

 substances have been prepared by the synthesis of their 

 inorganic elements. The most recent advance in this direction 

 is that of F.mile Fischer, who has produced polypeptides having 

 the same reactions as the peptones, by combining a number of 

 molecules of the amides of the fatty acids. 



In the further synthesis of organic compounds the problems 

 we have before us are of the same order as I hose already 

 solved. There is no essential difference between organic and 

 inorganic chemistry ; living organisms are formed of the 



