PROTOPLASM 9 



III. Chemistry. It is impossible to analyse such an ever- 

 changing substance as protoplasm, and although what is left 

 when these chemical changes are stopped can be examined, 

 such analyses give little insight into the essential nature of 

 the living matter. 



That substances of great complexity take part in the con- 

 stant whirl is shown by the analyses of what is left after 

 death. Five or six elements carbon, hydrogen, oxygen, 

 nitrogen, sulphur, and phosphorus are present, and these 

 are linked together to form molecules of enormous size. 



Water is the most abundant constituent of protoplasm, 

 amounting, as it does, to about 75 per cent. 



The Solids, constituting the remaining 25 per cent., con- 

 sist chiefly of a series of bodies closely allied to one another 

 and called " chief substances " or Proteids. In addition to 

 these, certain inorganic salts are found in the ash when 

 protoplasm is burned, indicating the presence of POTASSIUM 

 and CALCIUM along with PHOSPHORUS and SULPHUR. Small 

 and varying quantities of FATTY SUBSTANCES, and of CARBO- 

 HYDRATES, with traces of a number of other organic sub- 

 stances which need not here be enumerated, are also usually 

 present. 



Of these substances the Proteids alone have to be con- 

 sidered here, since they constitute the really important part 

 of the material. 



PROTEIDS 



White of egg may be taken as an example of such pro- 

 teids dissolved in water with some salts. If the salts be 

 separated, and the water carefully driven off at a low 

 temperature, a pure proteid is left. 



(A) Physical Characters. Proteids have a white, yellow, 

 or brownish colour. In structure they are usually amorphous, 

 but many have been prepared in a crystalline condition, 

 and it is probable that all may take a crystalline form. 

 The crystals vary in shape, being usually small and needle- 

 like, but sometimes forming larger rhombic plates. Some 

 proteids are soluble in water, others require the presence 

 of neutral inorganic salts, others of an acid or alkali, 

 while some are completely insoluble without a change 



