82 "COEFFICIENT OF DIFFUSION OF CELLS" 



ascertaining experimentally the lowest sum of units 

 of the factors both chemical in the jelly and physical 

 as applied to the slide which will just cause the 

 cell's nucleus to stain. In the original paper, already 

 referred to, which specified this method and the co- 

 efficients of diffusion, the following definitions were 

 given : 



When a film of agar jelly contains stain and 

 other substances, its Index of Diffusion (/#) may be 

 defined as the sum of its constituents, which delay 

 diffusion subtracted from the sum of its constituents 

 which accelerate diffusion added to the quantity of 

 stain contained in the jelly. 



The Coefficient of Diffusion (c/) of a cell is that 

 Index of Diffusion plus the time and temperature 

 required to cause staining of the nucleus, or staining 

 of the cytoplasm in unnucleated cells (e.g. red cor- 

 puscles), when the specimen is prepared by a standard 

 method. 



It should be noted that the index of diffusion 

 refers to the composition of the jelly, and that the 

 coefficient of diffusion refers to the rate at which 

 the cell absorbs substances from the jelly. 



The standard method of placing the cells on the 

 jelly-film and the general principles of preparing the 

 film have already been described. The cells are mixed 

 with a little "citrate solution" (3-per-cent sodium 

 citrate and 1-per-cent sodium chloride), which acts 

 as a vehicle to keep them alive, and in which they 

 are placed on the cover-glass. Since this citrate solu- 

 tion spreads to the periphery of the cover-glass, it does 



