2 THE CELL AS A PHYSICO-CHEMICAL UNIT 



Cytochemical Aspects 



In Fig. I (facing page i) are given diagrams of the cyto- 

 chemical distribution of a number of different substan- 

 ces in the hepatic cells of the liver. The diagram shows 

 the distribution of hydrogen ions, SH groups, nucleic 

 acids, glycogen, alkaline phosphatase, acid phosphatase^ 

 lipoids, and long chain aldehydes. These are the main 

 substances the distribution of which has so far been 

 revealed either by physico-chemical studies on cells, 

 or by cytochemical studies on cells. The distribution of 

 these various substances, and the concentration in par- 

 ticular places of these substances, is much affected by 

 the physiological condition of the animal, and by diet 

 and other factors extrinsic to the cell. Nor are all the 

 hepatic cells identical. Even in any particular lobule of 

 the liver, one sees marked differences between the cells 

 which are present at the periphery of the lobule and 

 those cells which are clustered round the central vein. 

 This difference is quite striking with pentose nucleic 

 acid, glycogen, alkaline phosphatase, and long chain al- 

 dehydes. On the other hand, there is comparatively 

 little difference in the desoxyribose nucleic acid con- 

 tent of hepatic cells in different positions in the lobule 

 and the total concentration of desoxyribose nucleic acid 

 is known to be comparatively little affected by extrinsic 

 factors. 



Even when so few substances as those mentioned 



