lir£^ 



THE BEGINNINGS OF LIFE. 



37 



' ^^'ith other 



transmit 



St: 



St 



'hich they 



stimulus calls into play the contractility of a muscle, 

 and so gives rise to a motor act. 



As we have already seen in respect to the muscle, 

 that its contractility lasts for a varying period after the 

 death of the animal, so is it in the case of the nerve. 

 This, after the death of the animal, is still capable of 

 transmitting a stimulus — a fact which is shown by its 



tivity. The 



are power (when stimulated) of calling into action the muscle 



{ 



to which it is distributed. The precise length of time 



1 



have abuni during which the property survives increases also in pro- 

 portion as the animal is low in the scale of organization. 



H. Lewes -J ! 



difference in Again, there are many experiments of the most striking 

 and motor H: ^^^^^ ^^ record which show the complete dependence of 



r 



alike is tliet "^^ nervous system upon a due supply of arterial blood. 



c 



\ for this 



^urlUtj. Nea' 



Without this all nerve-functions soon cease in parts 

 thus cut off from their stores of potential energy. The 

 experiments of many observers have shown that, when 



rtv of a nefft ^ . ' ■ 



^ ^ the posterior part of the body of a mammalian animal 



•onertYofaB . , 



^^ ^ has been cut off from its blood supply by ligature of 



vhen a s \ ^^ abdominal aorta, the complete insensibility and 



lated, is*^^ disappearance of all reflex'^ excitability which 



ich the stini supervenes, may be made to, cease in the course of a 



soon 



rses 



the ^^' 





Upon 

 quantity 



1% 



ofrf 



few minutes by the removal of the ligature from the 



r 



main artery. The renewal of the circulation of the 

 blood through the grey matter of the spinal cord re- 



tion? '^^'^ stores to this and to the paralysed parts generally their 



lating 

 direction, 



tbct 



^ That is to say, the ability to give rise to movements, in response to 

 external stimuli, through the intervention of lower nerve-centres, in- 

 dependently of the action of Will or volition. 



0. 20' P' 



34 



? 



