86 "COEFFICIENT OF DIFFUSION OF CELLS" 



Since it is essential that all jellies must be alike 

 in all respects except in the actual quantities of the 

 chemical substances which are to be tested on the cells, 

 it follows that every jelly-film is always made from 

 10 cc. of jelly. A film is never made direct from a tube 

 of 5 cc. of "coefficient jelly" unless it previously has 

 had added to it an equal quantity (5 cc.) of some 

 solution. If this rule is followed, every jelly-film 

 w T ill be identical in that the strength of the agar will 

 be the same, and the initial strength of the salts and 

 acid will be the same; but since the second 5 cc. may 

 be composed of any solution, each 10 cc. of jelly may 

 also contain a variety of other substances. 



It is in the extra 5 cc. of solution or solutions that 

 the chemical substances, with which one wishes to 

 experiment on the cells, and any chemical factors 

 additional to those already contained in the "coefficient 

 jelly" which are required to increase or decrease dif- 

 fusion, are added to that "coefficient jelly." 



The chemical factors, therefore, such as alkalies 

 and salts, which increase or decrease diffusion assist 

 to constitute the second 5 cc. of jelly which is always 

 added to the 5 cc. of "coefficient jelly." Now, one 

 could, of course, weigh out the right number of units 

 of each factor for every experiment, but it is much 

 simpler to add them from standard solutions. These 

 standard solutions should be kept ready to hand in 

 flasks, on the labels of which should appear the exact 

 amount of each which constitutes one unit. 



The 'same may be said of the chemical substances 

 the action of which one wishes to try on the cells. 



