THE ACTIVE FORCES OF LIVING ORGANISMS 69 



action and respiratory movements when one is walking 

 or running. These conditions in their bearing on 

 nervous action are, it is clear, somewhat abnormal, 

 and unless neutralized or counteracted may be pre- 

 judicial. 



The degree of ability to contract in a normal and P™:.,., 

 not excessive manner is, in a certain measure, a criterion 

 of the vitality of the tissues, and it is interesting to 

 inquire in what way, if at all, this power may be 

 developed. The problem is certainly a very difficult 

 one. We know in the first place that, in contracting, 

 any tissue must pass from a .state of higher to one of 

 lower oxidation. We also know that the degree of 

 oxidation in the tissues is dependent on the mode 

 of vibration of the nerve-cells, which control meta- 

 bolism in the parts they supply. This being so, if 

 the nerve-cells are by artificial means raised for a 

 time to a state of increased oxidation, and then 

 allowed, as the effect of the stimulus passes off, to 

 sink little by little to a slower state of oxidation, the 

 metabolism of the parts with which they are connected 

 will, in a healthy subject pari passu, undergo similar 

 changes. The inevitable nature of this change in 

 nervous vibration was pointed out in dealing with 

 physiological reaction, and though slight increases 

 and decreases of oxidation and of contraction or 

 expansion of the tissues are normal events, it is very 

 essential to keep them within the fairly narrow limits 

 of a healthy state. When the system has gone beyond 

 these limits, recovery may to some extent be caused 



