FIG. 24. Ehrlich at the age of 24. At about this age he dis- 

 covered the fundamental differences between basic and acid 

 dyes in their reactions with the constituent parts of cells, and 

 also showed how the varying permeability of these parts 

 aided differential dyeing, 



(From Marquardt,^-* by kind permission of Messrs William Heine- 

 mann Medical Books, Ltd.) 



