156 THE PATH OF SCIENCE 



and inorganic compounds. Raspail was making advances 

 by applying chemical color tests to thin sections of plant and 

 animal tissues, and the word protein was coined. Just at 

 the end of the forties, however, a striking technical advance 

 w^as made, which greatly encouraged the study of structure 

 while turning attention away from the study of substance. 

 This was the rediscovery of staining. Dyes had been used 

 sporadically in biological microtechnique a long time before, 

 but the biologists of the day did not know this. One after 

 another they began to rediscover what had been forgotten 

 and to apply it very much more actively than it had ever 

 been applied. The different constituents of tissues and cells 

 have extraordinarily different affinities for different dyes; and 

 by a little experimenting one can soon learn to make one part 

 of the cell stain in one color and another part in another. 

 One of the great difficulties in studying protoplasm had been 

 its transparency. That difficulty was now removed at a stroke, 

 and a clear insight was given into the minute structure of 

 organisms. 



Dyes, unfortunately, tell us little about chemical composi- 

 tion, and the study of substance soon became overshadowed 

 by that of structure. Raspail's work with real chemical tests 

 was overlooked, and microscopists began to become amateur 

 dyers. Then came Darwin with his Origin of Species; and 

 morphology— the study of form— received a second powerful 

 stimulus. People began to think that the main purpose of 

 biology was to exhibit the evolutionary relationships of or- 

 ganisms, and that could be done by the study of structure, 

 without much attention being paid to substance or function. 



In recent years there has been a healthy tendency to revert 

 to the study of substance instead of concentrating exclusively 

 on structure. All sorts of interesting^ methods have been 

 used to find out more about the actual substances of which 

 cells are composed. Some of these methods are actually new; 

 others are revivals of very old ones. One of them, micro- 

 incineration, actually originated with Raspail in the eighteen 

 twenties but has only recently been developed. Thin slices 



