4 THE CELL AS A PHYSICO-CHEMICAL UNIT 



shown up by c5rtochemical investigations are not all of 

 then; physically necessary for the maintenance of the 

 life of the cell. Insofar as there are absolutely unchange- 

 able centres of organisation in the cell, these must be 

 based upon the formed bodies of the cell such as chro- 

 mosomes, mitochondria, the cell and the nuclear mem- 

 branes, and the cell granules. The evidence at present 

 available shows that as long as these bodies are left 

 intact, the cell can recover from quite violent treatment 

 and disturbances of its normal chemical condition. But 

 this does not mean that the distribution of chemical 

 substances which we see in the cell under normal con- 

 ditions is of no consequence. Although cell constituents 

 may be rearranged by centrifugation or by micro-dis- 

 section procedures without killing the cell, there is a 

 certain amount of clear evidence showing that the acti- 

 vity of the cell is no longer carried on in the same way 

 during the period in which this redistribution exists. 

 Thus Bracket has shown that the cyanide-sensitive 

 respiration of amphibian liver is eliminated by strati- 

 fication in the centrifuge, but returns when the cell con- 

 stituents have been restored to their normal positions. 



Cytoplasmic Gels 



Except during mitosis, protoplasmic gels do not play 

 a very obviously prominent part in the activity of he- 

 patic cells. But in a variety of other cells experimental 



