THE COLLOIDAL STATE. 67 



to facts which furnish a welcome support of this concep- 

 tion in the physiology of the senses. 



As early as 1865, through his complete recognition of the 

 relation between the physical and psychic elements of a 

 sensation and through the assumption that every quality of 

 a sensation has lying at the bottom of it a specific change 

 in the substance of the nerve, which for the same sensation 

 is the same, and for similar sensations partly identical. 

 E. MACH laid the foundations from which, through an 

 analysis of the sensations, a knowledge of the changes 

 that go on in living matter has been obtained. In his 

 hands and through the work of E. HERING, who, some- 

 what later and independently of MACH, set up the same 

 principle of research, this led to a great enrichment of 

 the physiology of the senses. Upon these same founda- 

 tions HERING has built up his famous theories of the 

 sense of light and color, a theory of the temperature sense, 

 and finally a general theory of the changes that go on in 

 living matter. The great and fruitful significance that 

 these principles possess, not only for questions in the 

 physiology of the senses, but also for general physiology 

 and for a recognition of the aims and limits of scientific 

 research in general, could only temporarily be belittled, 

 through the mighty authority of a HELMHOLTZ. To-day 

 when this combat is a thing of the past and the teaching 

 of MACH and HERING has made itself felt in the most 

 varied branches of science, we recognize that in decades 

 general physiology has enjoyed no such significant increase 

 in enlightenment as has been furnished by the MACH- 

 HERING analysis of the sensations and the physical changes 

 that lie at the bottom of these sensations. 



We will enter into this physiology of the senses only 



