METHOD OF DETERMINATION 91 



It is kept in quantities of 5 cc. in test-tubes ready 

 to hand. Each "coefficient jelly" contains sufficient 

 salts for cells to live on it; it is acid to the extent 

 of 2 units; and another 5 cc. of some solution must 

 be added to it before it is poured on to a slide to make 

 the "jelly-film." The film is always made from 10 cc. 

 of jelly. 



In experimenting with a certain class of cells, 

 one must in the first instance always estimate their 

 coefficient of diffusion. The cells are mixed with 

 "citrate solution" and kept ready at the room 

 temperature, preferably in the revolving apparatus 

 (see Chapter II.). 



In order to determine the coefficient of diffusion 

 of these cells a tube of "coefficient jelly" is taken and 

 a few units of stain are added to it, together with 

 2 or 3 units of alkali solution. The content of the 

 tube is then completed up to 10 cc. with water. The 

 tube is steeped in the beaker of boiling water until the 

 "coefficient jelly" all melts, when the stain and alkali 

 become mixed with it, as will be presently described. 

 A film is prepared from it on a slide, and a drop of the 

 citrate solution, with the cells in suspension, placed on 

 to it under a cover-glass. The specimen is kept at a 

 certain temperature representing a certain number of 

 units of heat until a certain number of minutes repre- 

 senting a certain number of units of time have elapsed, 

 and then the specimen is examined under the micro- 

 scope. If the nuclei of the cells are not yet stained, a 

 few more minutes (e. g. another unit of time ten min- 

 utes) are allowed. If, then, the nuclei are not stained, 



