100 HUMAN PHYSIOLOGY 



cannot be roused to meet an emergency. Central re- 

 sistance must be of a medium grade if all is to go well 

 with the individual. 



A subject who is described as " nervous" is one whose 

 resistance is more or less lowered from the normal. He 

 will be unreasonably disturbed by external conditions 

 which a more robust person readily ignores and he will 

 tire himself by countless reactions which were better 

 not carried out. Low resistance is seen to be opposed 

 to conservation of one's resources. It is undoubtedly 

 more common as a constitutional fault than a high 

 resistance which must be indicated by stolidity of 

 temperament. 



Resistance and Coordination. Reflex acts are, in 

 most cases, clearly coordinated. That is to say, a 

 number of muscles are used in their execution and their 

 effects are combined for a common end. Some muscles 

 bear the brunt of the duty while others support them 

 inconspicuously. Certain ones act in advance of others, 

 for coordination is a matter of sequence as well as of 

 combination. The facts observed can be explained 

 upon the basis of " graded synaptic resistance." When 

 a stream of afferent nerve-impulses enters the central 

 gray matter many possible ways lie open to their further 

 flow. But some of these paths are relatively easy and 

 others difficult. The impulses which find a free pas- 

 sage dictate the more powerful muscular responses; 

 those which encounter a greater hindrance find a more 

 limited expression on the efferent side. 



It has been shown that the convulsions of strychnin 

 poisoning, already referred to, are the result of a re- 

 duction of resistance in the central stations such that 

 the paths which are ordinarily impossible to penetrate 

 are freely opened while those that have normally a 

 high resistance come to have no more than the beaten 

 tracks. We should anticipate just such a result as that 

 which we actually see, opposing muscles straining use- 

 lessly, one against another. 



