THE STAINING OF A CELL 43 



a watch-glass. A drop of the cell-containing mixture 

 is then placed on to the cover-glass and similarly placed 

 upon the jelly. 



The citrate solution simply acts as the vehicle 

 in which the cells are kept in a living condition before 

 being placed upon the jelly, and furthermore, by dilut- 

 ing the blood, . it reduces the actual number of cells 

 which come to rest in any field of the film. If no 

 citrate solution is used they are apt to become huddled 

 or crowded together owing to their great numbers, 

 and the leucocytes may become completely hemmed 

 in by erythrocytes so that a clear observation of the 

 whole cell cannot be obtained. 



We must now pass on to the study of some of 

 the phenomena connected with the staining of the 

 cells, which have been the means of elucidating many 

 cytological details which have led to the correct 

 appreciation of the effects of chemical substances on 

 cells. In this chapter, however, I do not propose to 

 discuss very deeply the actual laws by which the 

 staining of the cells is controlled; that will be reserved 

 for discussion when I come to speak of the diffusion 

 of the substances, including stain, into the cells. In 

 the meantime I shall simply describe what happens 

 to the cell as it absorbs the stain (say Unna's 

 polychrome methylene blue, Grubler) ; how the stain 

 causes the gradual death of the cell (the staining of 

 the nucleus invariably kills it) and how death is 

 followed by achromasia. The amount of stain which 

 is put into any given jelly is not added in a hap- 

 hazard way, the actual amount necessary to cause 



