THE FACTORS CONCERNED 69 



Briefly, therefore, we may say that the diffusion is 

 proportional to the amount of substance diffusing, or 

 we may plot it thus: 



diff = S 



Obviously, the diffusion of a substance into a cell 

 takes time. If there is only sufficient dye to combine 

 with a certain amount of protoplasm, the combination 

 will occur in a certain time, and then the diffusion will 

 cease, for all the dye will be used up; but if there is 

 a sufficiency of stain for it to go on diffusing indefi- 

 nitely into the cell until it kills it by staining the 

 nucleus, then the diffusion will go on for a longer 

 time in fact, it will go on diffusing minute after 

 minute until death occurs. Hence W T C may say that 

 the longer the time which we observe the diffusion, the 

 greater will that diffusion be, unless the substance is 

 all used up a contingency which in reality cannot 

 occur in practical experimentation, but it may occur 

 in the body. It must be remembered that once the 

 experimental jelly- film is made it cannot be altered, 

 whereas in the body there can be no doubt that the 

 solutions are being continually modified during meta- 

 bolism. 



With a given concentration of dye or other sub- 

 stances in the jelly, therefore, the greater the time 

 during which the cell is resting on the jelly, the more 

 of that substance will diffuse into the cell, also in 

 direct arithmetical proportion. Each minute will see 

 an equal amount of substance diffusing, provided the 

 supply of that substance is constant, and that other 

 conditions remain the same during the time. 



