EXPRESSED AS AN EQUATION 79 



proportion to the increase caused by one unit of alkali, 

 dye, or time. All the units are equal to each other 

 as regards the increase or decrease of diffusion, and 

 therefore they are interchangeable. Hence we may 

 simplify our equation by adding together all the units of 

 all the factors and making a grand total of them ; thus : 



=13-3, 



or, simpler still: 



c/ = 10. 



This method of determining the coefficent of 

 diffusion is intended principally to assist experimenta- 

 tion with these in-vitro technics. The act of its 

 determination gives up the comparative rate of the 

 diffusion of other substances into the cells under 

 observation, and tells us how to prepare jellies for 

 further experimentation with these substances. For 

 practical purposes, the equation and the measurements 

 of the units of the several factors (w T hich are used 

 continually, not only in the initial determination of the 

 coefficient of diffusion, but in all subsequent experi- 

 mentation) have been devised with a view to the 

 simplification of the practical methods to be described 

 in the next chapter, w r here full details for the prepara- 

 tion of the jellies, etc., will be stated. These laws of 

 diffusion were ascertained in the first instance by me 

 with the jelly method as described in the paper in the 

 Journal of Physiology already referred to, and they 

 soon led to the method of determining the coefficient 

 of diffusion by the same method w r hich was published 

 in a paper in the Proceedings of the Royal Society 



