CHAPTER II 



CHEMICAL SIGNS OF IRRITABILITY IN THE 



NERVE FIBER 



There are various chemical processes which occur in 

 all forms of living matter and which we might examine 

 in order to see whether they are associated with the 

 property of irritability, but we naturally seek to make 

 use of that one which is the easiest to detect. Among 

 these chemical processes there are, in the first place, 

 the processes concerned in growth. All living matter 

 has the power of building up complex proteins, fats, 

 and carbohydrates as long as it is vigorously alive. 

 But it is clear that this process would be very hard to 

 measure quantitatively without killing the living matter 

 and determining how much substance it has produced. 

 And there are also other objections to using growth as a 

 measure of vitality. Another chemical process found 

 in all, or nearly all, forms of matter is respiration. By 

 respiration we mean the gaseous exchange of living 

 matter with its environment: the taking on of oxygen 

 and the production of carbon dioxide. This is a very 

 much more promising line of experiment to follow in 

 measuring life and metabolism, for, in the first place, it 

 is universal, as I shall presently show, and, in the second 

 place, the oxygen may be measured, or the carbon 

 dioxide given off may be determined, without injuring 

 the living matter. It was for this reason that the 

 carbon dioxide was selected for study as probably 



IO 



