2 THE SCOPE OF THE NEW METHOD 



to experiment with, and which has, while in a molten 

 condition, been poured on to a microscope slide and 

 allowed to set there. The jelly may, for instance, 

 contain an aniline dye; and by watching the way in 

 which the living cells absorb the stain from the jelly, 

 and by experimentation with it, many of the laws of 

 the diffusion of substances into living cells have been 

 ascertained; and by the application of these laws we 

 can now add other substances to the jelly and make 

 them also diffuse into the living cells, and watch the 

 results by means of the microscope. The cells are 

 pressed into the jelly by the cover-glass, and therefore 

 they can absorb only what is in the jelly (there is 

 nothing else for them to take), provided that the 

 conditions have been correctly arranged for the pass- 

 age of the substances from the jelly into the cells. It 

 is essential to note that one class of cells differs from 

 another with reference to the rate at which they absorb 

 materials from the media in which they are placed, so 

 that the composition of any given jelly must be cor- 

 rectly arranged for experimentation with any particular 

 class of cell with which it may be desired to work. 



The word "cell" in this book refers to the living 

 cell unless otherwise specified. Cells must always be 

 freshly removed from the body when they are placed 

 on the jelly. It occasionally happens that the cells 

 may have just died or be dying when they are ex- 

 amined, as when mitotic divisions are being induced 

 by azur stain, as will presently be described; but, 

 generally speaking, after the cells in a specimen are 

 dead the specimen is thrown away. It is obvious 



