go THE ACTIVE FORCES OF LIVING ORGANISMS 



oxidation. This is chiefly important because of the 

 relation which anabolism, or the building up of tissue, 

 bears to the general state of contraction of both the 

 arterial system and the tissues, together with the 

 nervous metabolic rhythm. If the arteries, instead 

 of being normally contracted, are too relaxed, the 

 tissues coming under the same general influence will 

 be too relaxed, and the metabolic rhythm of the 

 nerve-cells on which the metabolism of the tissues 

 depends will be too relaxed also. The holding power 

 of both the tissues and the nerve-cells will therefore 

 be diminished, and metabolism in them, though 

 not wholly katabolic, will nevertheless inchne to 

 the side of katabolism rather than to that of 

 anabolism. 



If we admit that expansion and contraction are 

 essential elements in metabolism, either owing to the 

 relations existing between the vaso-motor centres and 

 the rest of the nervous system, or for reasons of a 

 more direct nature, we may compare nervous action 

 in general to the behaviour of a piece of elastic band 

 at rest or under tension. You cannot make the band 

 contract unless you have previously stretched it ; but 

 the more you stretch it, especially if you overstretch 

 it, the less forcibly in the end will it contract. By 

 degrees, as it becomes worn out, it will appear drawn 

 together and crinkled, and is weak and limp. So it is 

 with the nerve-cell. At first, we may suppose, it is 

 well filled and plump, but by intense vibratory action 

 accompanied by an excessive blood-supply, which ia 



