34 BORDER LINES OF KNOWLEDGE 



"Just as a tree constitutes a mass arranged in a definite 

 manner, in which, in every single part, in the leaves 

 as in the root, in the trunk as in the blossom, cells are 

 discovered to be the ultimate elements, so is it also with 

 the forms of animal life. Every animal presents itself 

 as a sum of vital unities, every one of which manifests 

 all the characteristics of life."* 



The mechanism is as clear, as unquestionable, as ab- 

 solutely settled and universally accepted, as the order 

 of movement of the heavenly bodies, which we com- 

 pute backward to the days of the observatories on the 

 plains of Shinar, and on the faith of which we regulate 

 the movements of war and trade by the predictions of 

 our ephemeris. 



The mechanism, and that is all. We see the work- 

 man and the tools, but the skill that guides the work 

 and the power that performs it are as invisible as ever. 

 I fear that not every listener took the significance of 

 those pregnant words in the passage I quoted from 

 John Bell, — '^ thinking to discover its properties in its 

 formP We have discovered the working bee in this 

 great hive of organization. We have detected the cell 

 in the very act of forming itself from a nucleus, of 

 transforming itself into various tissues, of selecting the 

 elements of various secretions. But why one cell be- 

 comes nerve and another muscle, why one selects bile 

 and another fat, we can no more pretend to tell, than 

 why one grape sucks out of the soil the generous juice 



* Virchow, Cellular Pathology, Lect. I. ^ 



