168 THE NERVOUS SYSTEM. 



chloroform, be raised, and then allowed to fall, it will be 

 noticed that the limb does not drop instantly, like a life- 

 less member, but a certain amount of rigidity remains -in 

 its muscles, which resists or breaks the force of its descent. 

 Again, when a substance like melted sealing-wax, or a 

 heated coin, falls upon the hand, the limb is snatched 

 away at once, even before the feeling of pain has been 

 recognized by the brain. When jolted in a rapidly moving 

 car, we involuntarily step forward or backward, so as to 

 preserve the centre of gravity of the body. 



42. These and similar acts are executed by the same 

 mechanism as that previously described in the case of 

 paralysis from an injury of the spinal cord. The muscles 

 thus called into play, are those which are ordinarily under 

 the sway of the will, but which in these cases act through 

 this reflex action of the cord, altogether independently of 

 the will. A healthful reflex activity produces an elasticity, 

 or " tone," of the voluntary muscular system, which, in a 

 great measure, explains the existence in the young and 

 vigorous of a feeling of buoyancy and reserve power. Its 

 possessor is restlessly active, and it may appropriately be 

 said of him, "he rejoiceth as a strong man to run a race." 

 But this reflex energy may be deficient. This is true when 

 the blood is poor and wanting in its solid ingredients, or 

 the circulation is feeble ; the muscles, then, are flabby and 

 weak, and the person himself is said to be " nerveless," or 

 indisposed to exertion. Shivering from cold, and trem- 

 bling from fear, may, in part, be referred to a temporary 

 loss of tone, resulting from a powerful impression upon the 

 brain- 



43. An excess of this activity may also be observed in 

 disease. In this condition, the excitability of the cord is 

 unnaturally aroused, and frequent and violent movements 



42. Result of healthful reflex activity ? When may the reflex energy he defl- 



43. Excess of this activity in disease ? Hydrophobia, etc. ? The difference in 

 severity of the convulsions " 



