Functions of (fu j Spinal Cord. 605 



CHAPTER LlX. 



FUNCTIONS OF THE SPINAL CORD. 



Having, in the foregoing chapters, got some idea of the construction 

 of the rather complicated miichinciy of brain and nerves through which 

 the animal organism is regulated and 'directed, it will be our next en- 

 deavor to find out how this machinery works and what runs it. 



There are several means by which the functions of the several parts 

 of the brain and nervous centers are ascertained. One is by compari- 

 son of the human brain and nervous system with that of the lower ani- 

 mals, and by observing in connection therewith the contrasts and cor- 

 respondences of nervous and mental action. Another is by experiments 

 on the nervous system with direct stimuli. In the case of the lower 

 animals these experiments are often accompanied by the artificial de- 

 struction of one part or another of the nervous apparatus, and observa- 

 tion made of the functions lost to the animal by such destruction. In 

 man the same end is accomplished when accident or disease injures or 

 destroys SOUK- function, which postmortem examination subsequently 

 connects with a lesion of sonic special part of the brain or nervous gan- 

 glia. In experimenting with animals it is practicable, in many cases, 

 to cut away the cerebrum, or to sever the spinal cord at any point be- 

 low the cervical vertebra without immediate destruction of life. Those, 

 lesions of the spinal cord which result in paralysis, amount temporarily 

 to the same thing as the severing of the spinal cord. There have been 

 numerous cases of this kind, from the observation of which it has been 

 well settled that the spinal cord by itself possesses the necessary ma- 

 chinery for deflecting a stimulus from the environment back to the mus- 

 cles of the limbs. And the cord being, for the time, practically discon- 

 nected from the parts of the upper nervous centers, which are the seat 

 of sensation and consciousness, these reflected stimuli produce action in 

 the limbs or muscles without its being felt or perceived by the patient, 

 or in any way controllable by his will. 



Carpenter cites a case of paraplegia, or paralysis of the lower half 

 of the body, resulting from injury to the spinal cord in the dorsal re- 

 gion. The lower limits had lost nearly all sensibility and power of vol- 

 untary motion. But. when a limb was pinched or pricked, it jumped, 

 the muscles being contracted so as to draw upward the toes and foot, 

 bend the knee and raise the whole limb. These stimuli might be per- 

 ceived by the patient, but if the sole of the foot were tickled by a 

 feather, of which stimulus the patient might be unconscious, the con- 

 vulsions would be still more violent, and of course unconl rollable. The 



