74 DIFFUSION OF SUBSTANCES INTO LIVING CELLS 



the same conditions, when it may be found that now 

 no staining, or less staining, may take place. If one 

 adds more stain or more alkali, or more heat, or allows 

 more time, this second class of cells may then stain. 

 Hence we may say that the second class of cell has 

 a higher "coefficient of diffusion" than the first, for 

 it requires more of one or more factors which increase 

 diffusion to cause a certain extent of diffusion into 

 it than did the first class of cells. Different classes 

 of cells may therefore each have different coefficients of 

 diffusion, but in spite of this fact the diffusion of 

 substances into all classes of them depends on the 

 factors already expressed by the equation: 



diff = S+T+H + A-salts. 



That is to say, that the factors given in the equation 

 increase or decrease the diffusion of substances into 

 all cells; but some classes of cells require more or 

 less of them to cause the same amount of diffusion 

 than do others. 



It is obvious, therefore, that we must always find 

 the coefficient of diffusion of a class of cells before we 

 can attempt to make substances diffuse into them; and 

 we find the coefficient of diffusion by ascertaining the 

 number of the factors expressed in the equation, and 

 the amount of each of them required to cause a certain 

 extent of staining of the cell. By means of the equa- 

 tion we can set down algebraically the number of 

 factors and the amount of each of them required to pro- 

 duce this certain extent of staining; and then they are 



