ON THOUGHT IN MEDICINE. 231 



natural elements ; whether the so-called pure or the 

 empirical, the axioms of geometry, the principles of 

 mechanics, or the perceptions of vision. For this 

 reason, therefore, the mathematical investigations of 

 Lobatschewsky, Gauss, and Riemann on the altera- 

 tions which are logically possible in the axioms of 

 geometry; and the proof that the axioms are principles 

 which are to be confirmed or perhaps even refuted by 

 experience, and can accordingly be acquired from ex- 

 perience these I consider to be very important steps. 

 That all metaphysical sects get into a rage about this 

 must not lead you astray, for these investigations lay 

 the axe at the bases of apparently the firmest supports 

 which their claims still possess. Against those investi- 

 gators who endeavour to eliminate from among the per- 

 ceptions of the senses, whatever there may be of the 

 actions of memory, and of the repetition of similar im- 

 pressions, which occur in memory; whatever, in short, 

 is a matter of experience, against them it is attempted 

 to raise a party cry that they are spiritualists. As if 

 memory, experience, and custom were not also facts, 

 whose laws are to be sought, and which are not to be 

 explained away because they cannot be glibly referred 

 to reflex actions, and to the complex of the prolonga- 

 tion of ganglionic cells, and of the connection of nerve- 

 fibres in the brain. 



Indeed, however self-evident, and however important 



