22 WHAT IS LIFE 



there is floating a small glass sphere as big as say 

 a Tangerine orange, and that inside this sphere 

 are some tangled skeins of red tape floating in a 

 further mass of unboiled white of egg. He will 

 then have constructed a mental model of a general- 

 ised cell. The air-balloon will represent the cell 

 wall and the white of egg within the cell : protoplasm 

 or cytoplasm. The contained sphere will represent 

 the nucleus and the skeins of red-tape the chro- 



Nucicu matin skeins which it contains. The nucleus is 

 generally though not at all times included in a 

 nuclear membrane which is to it what the cell- 

 wall is to the cell. Within this membrane is a 

 reticulum or net-work, a ground substance or 

 nuclear sap and often one or more nucleoli. 



Of all these portions the most essential is the 

 reticulum which consists of two parts, a general 

 protoplasmic basis, or linin, which closely resembles 

 cytoplasm, and a second constituent known, from 

 its faculty of staining deeply with certain re-agents, 



Chromatin as chromatin. There are some who maintain that 

 the interstitial protoplasm is the most important 

 part of the nucleus, but the great weight of scientific 

 opinion at present inclines to the view that the 

 chromatin fragments are the essential part not 

 only of the nucleus but of the whole cell. It 

 seems as if it were the only part of the nucleus 

 which is specifically sorted out so as to be handed 



