Chapter V 



PHYSICO-CHEMICAL CONSTITUTION 

 OF THE CYTOPLASM 



The cytoplasm, as has been seen earlier, appears to be con- 

 stituted essentially of proteins (68.8% of dry weight), water- 

 insoluble lipides (about 15% of dry weight), and a large propor- 

 tion of water (80-90% of fresh material) containing various 

 mineral substances in solution. It may be considered then as a 

 colloidal solution whose micelles are represented by protein mole- 

 cules united with lipide molecules, the intermicellar liquid being 

 water. 



It seems that every cell contains the same chemical constituents 

 and that differences between the cellular types exist only in the 

 proportions of the chemical constituents present. One is obliged 

 to admit, however, that each type of cell has a protoplasm, and 

 therefore a cytoplasm, which is peculiar to it. The widely-varying 

 properties of the plastids are identified not only by the differences 

 of minimum and maximum temperatures necessary for their 

 growth, but by the elaboration products of their protoplasm, which 

 differ essentially from one cell to another. The diverse properties 

 of different plants are due to the individual constitution of their 

 protoplasm and, in particular, of the cytoplasm which is peculiar 

 to each. One is therefore driven to the idea of specificity of proto- 

 plasm but chemical analysis has not so far furnished any basis for 

 this notion. Nevertheless, the possible number of different nucleo- 

 proteins being theoretically indefinite, it is admissable that each 

 species of animal or plant be characterized by a special nucleo- 

 protein. 



Electrical characteristics of proteins:- The work of MiCHAELIS, 

 Procter, Wilson, and especially of Jacques Loeb, confirming an 

 hypothesis formulated a long time ago, has demonstrated that the 

 proteins belong to the class called electrolytic colloids which behave 

 as ionisable electrolytes. Their micelles, seeming to correspond 

 to enormous molecules, ionize to form true micellar ions, or protein 

 ions, having an electric charge analogous to that resulting from 

 the dissociation of the valence bonds of an ordinary electrolyte. 



The proteins correspond to electrolytes called ampholytes, that 

 is to say, possessing at the same time acid and basic functions. 

 They are formed, as is known, of amino acids combined one with 

 the next, a great number of times, to form enormous molecules. 

 Now an amino acid may be schematically represented by the 

 following formula: 



