THE CONSTRUCTION OF PROTEINS 161 



a pure condition, too much stress must not be laid upon 

 the results obtained. These, moreover, are, as we should 

 expect, not altogether concordant. 



Analysis of a crystallised protein prepared from the 

 seed of the hemp showed it to have the following percentage 

 composition, which may be taken, within somewhat wide 

 limits, to be fairly typical of all. 



Carbon .... 51-58 

 Hydrogen .... 6*88 



Nitrogen .... 18-8 



Oxygen .... 21-65 

 Sulphur .... 1-09 



Besides containing these essential constituents, many 

 proteins leave on ignition a certain amount of ash. This 

 consists of small amounts of the chlorides, phosphates, sul- 

 phates, and carbonates of sodium and potassium, with traces 

 of the corresponding salts of calcium, magnesium, and iron. 

 It is not certain that these ash constituents are an integral 

 part of the protein jnolecule in any case ; the balance of 

 evidence points rather to their being impurities which are 

 very difficult of removal. 



Most of the proteins found in plants exist in an amor- 

 phous condition, and are very closely incorporated with 

 the protoplasm. In a few cases they are met with as 

 definite grains, and in certain reservoirs of food material 

 they occur as crystals. Some of them can be made to 

 crystallise after extraction from the organism, but many 

 forms exist which do not possess this property, so far as 

 we know at present. It is not certain, however, that the 

 crystals are always composed of pure protein only. 



The proteins vary very much among themselves as to 

 their solubility in water and other neutral fluids. Some 

 are soluble, others insoluble, in water ; some are soluble 

 in solutions of neutral salts of various degrees of concentra- 

 tion. Nearly all are insoluble in alcohol and ether ; they 

 all dissolve in strong mineral acids and in caustic alkalies, 



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