AN ABOLISH AND KATABOLISM. 29 



of assimilation of A gives us the sensation of black ; and similarly with 

 red and green for B, with yellow and blue for C. 



But generalising from his studies on colour sensation, Hering was led 

 to regard all life as an alternation of two kinds of activity, both induced 

 by stimulus, the one tending to storage, construction, assimilation of 

 material, the other tending to explosion, disruption, disassimilation. 

 Both processes are, according to Hering, activities ; both are dependent 

 upon stimulus ; they differ, however, in direction and results. 



In your future physiological studies you will also learn of the paths or 

 channels by which the brain sends its mysterious commands to the 

 various parts of the body. You will learn that some of these bear 

 impulses to activity, while others convey commands which send the 

 affected part to rest. 



It was in studying and greatly elucidating these interesting facts, that 

 Professor Gaskell was led to a theory of vital action somewhat different 

 from that of Hering. 



Gaskell believes that life means an alternation of two processes, one of 

 them a running down or disruption (katabolism), the other a winding 

 up or construction (anabolism). The disruptive or katabolic process in 

 which energy is discharged, takes place occasionally and in obedience to 

 stimulus ; the constructive or anabolic process of restitution goes on con- 

 stantly and of itself, i.e., without the necessity of stimulus. Thus 

 Gaskell's theory suggests an alternation of activity and rest, of stimulated 

 disruption and self-regulative construction, while Hering's theory 

 suggests an alternation of two antagonistic kinds of activity, assimilation 

 and disassimilation, both requiring stimulus. The student will find the 

 theories, which I have briefly noticed, discussed in Professor M. Foster's 

 article PHYSIOLOGY, in the Encyclopedia Britannica, and in an address 

 by Professor Burdon Sanderson (British Association Reports, 1889, and 

 also published in Nature, September 1889). 



