XIV.] ORGANIC FUNCTIONS. 161 



fibre to the muscle in wMcli the motion is to be produced, 

 in order to make the right response to the stimulus. 



Such actions as these are called reiiex, the nervous Keflex 

 action being, as it were, reflected back from the ganglion. ^''*^°°- 

 There can be scarcely a doubt that this is the only kind of 

 nervous action in those animals which have a nervous 

 system in its most rudimentary form — as, for instance, in 

 the lower mollusca. As we ascend in the animal scale, the 

 proportion of purely reflex actions appears to become con- 

 stantly smaller ; but even in man those muscular actions 

 which minister the most directly to the vegetative life are 

 of this kind. The actions of the heart, lungs, and stomach Reflex 

 are reflex, being independent of sensation or will : the ^earT ^^ 

 stimulus to action is given in the heart by the flowing in lungs, and 

 of the blood ; in the lungs, by the flowing in of the air ; in 

 the stomach, by the contact of the food. And actions 

 which are normally performed in obedience to sensation or Reflex 

 wUl may become reflex : thus, if the spinal cord (which is performed 

 a vast bundle of nerve-fibres, accompanied with ganglionic abnor- 

 cells) is so injured as to destroy all nervous connexion - 

 between the lower extremities and the brain, the lower 

 extremities cease to have any sensation, or to be under the 

 control of the will ; but the ganglionic masses of the spinal 

 cord act as a " reflex centre " for them ; and if the centri- 

 petal nerves are excited, as by tickling the soles of the 

 feet, the spinal cord, on receiving the unfelt stimulus from 

 the centripetal nerves, will reflect it back along the cor- 

 responding centrifugal nerves in the form of a motor im- 

 pulse, producing convulsive motions of which the patient 

 is totally miconscious. 



Next is what Dr. Carpenter calls consensual action : that Consen- 

 is to say, muscular action depending on sensation, but 

 involuntary; such as closing the eyes against a flash of 

 light, or shrinking from the contact of anything that cuts 

 or burns. Both reflex and consensual action are in re- 

 sponse to a stimulus ; but reflex action, as we have seen, 

 is independent of any sensation, while the stimulus to 

 consensual action consists in sensation. Cause of 



We do not know, and it is not probable that we ever uuknowr. 



M 



