OF VITAL MOTION. 113 



nervous force during the period of diastole; while, 

 according to the same rule, the period of feeblest 

 innervation will be during the systole, and the short 

 space of rest immediately antecedent. 



It may be objected, however, that the flow of blood 

 in the capillaries is uniform and regular, and not 

 intermittent, as is here supposed, and it is not to be 

 denied that this objection is of great importance. At 

 the same time it will be admitted that this uniformity 

 is only comparative. Whatever, indeed, may be the 

 case in muscular and firmer textures, it is difficult to 

 imagine uniformity in the softer nervous structures, 

 where the vessels are extremely delicate, and com- 

 paratively destitute of extraneous support. On the 

 contrary, the powerful pulsatory movements of the 

 brain that are consentient with the beats of the heart, 

 and which are seen when a portion of the skull is 

 removed, and felt in the throbbing torments of head- 

 ache, are arguments in favour of some variations in the 

 supply of blood to the brain at least, such as might 

 determine an intermittent development of nervous 

 influence. 



From the manner in which the blood is sent from 

 the heart, therefore, we may infer that the develop- 

 ment of nervous energy will be in corresponding 

 intermittent gushes: and here we begin to catch a 

 glimpse of the causes which operate upon the heart, 

 and produce its mysterious rhythm. Let us suppose, 



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