VITAL GROWTH AND CRYSTALLIZATION 37 



4. THE PROBLEM OF RELATION OF LIVING GROWTH TO CRYS- 

 TALLIZATION. CONDITIONS DETERMINING THE SIZE 

 OF GROWING CRYSTALS 



We hope to get a "glimpse into the workshop of nature'' 

 by studying crystalline forms produced in non-living matter 

 and comparing them with those of the living world. What 

 a diversity of forms of life-like appearance can crystalliza- 

 tion produce in lifeless matter! 



Now we wish to understand what occurs in living plants 

 or animals. Are their bodies formed by a process related 

 to crystallization? Before answering this question let it 

 be clearly understood that none of these gelatin structures, 

 or the various aggregates of crystals, can be called living. 

 Some of the most essential features of life are not shown at 

 all by any of them: all these structures lack the ability of 

 living plants or animals to build up their bodies from food 

 material which is totally different in composition from the 

 substances of their own bodies. A crystal can grow only 

 in its own solution. Sugar, for instance, will dissolve in 

 water, but in so doing it has not undergone any changes; 

 the sugar water tastes as sweet as the crystalline sugar. If 

 we drive off the water from the sugar solution by gently 

 heating it, the sugar is left behind, and appears again as 

 crystals in the same form as before. 



In spite of this profound distinction there is a general 

 similarity between living forms and those of certain crys- 

 tallized non-living materials. It would seem therefore that 

 a relation of some sort must exist between the growth of a 

 crystal and that of a living thing. The determination of 

 the nature of this relation ought to be looked upon as one 

 of the greatest tasks of science, but its solution has been 

 handicapped by the prejudice that only those substances 

 are crystalline in which crystals are directly visible. It is 

 easy to demonstrate, however, that crystals of any size can 



