"COEFFICIENT JELLY" 83 



not materially influence the diffusion of the stain from 

 the jelly into the cells. When experimenting with 

 blood-cells the blood is mixed with an equal volume 

 of the solution. In the case of other cells the mix- 

 ture is made as may be convenient. In some instances, 

 when the cells are naturally suspended in a fluid- 

 such as pleuritic fluid it is unnecessary to use any 

 citrate solution at all, and the cells may be placed, 

 suspended in their own fluid, straight on to the cover- 

 glass. 



The general principle of preparing the jelly-film, 

 as given in Chapter III., may be recalled. A 2-per- 

 cent solution of agar in water forms a jelly basis for 

 these experiments. This jelly is kept stored in large 

 test-tubes, so that small quantities of it may be used 

 without having to melt it in bulk every time some 

 is wanted; and it should be filtered when it is made 

 in a manner similar to that employed for the prepara- 

 tion of "nutrient agar," although, of course, it has 

 no "nutrient" ingredients added to it. 



As already mentioned, the 2-per-cent solution of 

 agar has such a consistency that it can, when melted, 

 be diluted with an equal volume of a liquid and yet 

 will set as a firm jelly on a slide when it cools. 



Experimentation with this method is essentially a 

 process by which one contrasts the effects of one sub- 

 stance on cells compared with those of others; hence it 

 is important that all the conditions must be the same 

 in each experiment, except the actual difference in the 

 amount of the substance which has to pass into the 

 cells. To this end the jelly-basis is always the same in 



