CHAPTER X. 



OF THOUGHT. 



WE are now about to explore a biological department which has 

 for centuries been the exclusive domain of metaphysical phantasy, 

 and which is still its sanctuary, its last refuge. The fact is, that 

 scientific investigation could not undertake with any success the 

 analytical study of conscious biological facts without being armed 

 at all points. It was first of all necessary to acquire, by patient 

 and innumerable researches, a just idea of organisation and of 

 life ; it was necessary to prove that the living world and 

 the mineral world are only diverse modes of an identical sub- 

 stance; to watch, step by step, the circular movement of 

 the material molecules ; to see them vitalised, then mineral- 

 ised, in the nutritive vortex ; to distinguish and co-ordinate 

 the great organic properties. At the same time, it was neces- 

 sary to unravel the anatomical structure and texture of all 

 living beings, to resolve them into systems, apparatus, organs, 

 tissues, and anatomical elements. That done, it was possible to 

 classify the functions, as we have classified the organs, and 

 especially to connect the fundamental properties of the living 

 substance with the tissues. "We have seen that all the anatomical 

 elements grow, are nourished and reproduced ; but that on this 

 general substance are grafted properties peculiar to each histo- 

 gical species, that the epithelial cell secretes, that the muscular 

 fibre contracts, that the nervous fibre conducts the motory and 

 sensitive incitations; finally, that all the phenomena of con- 



