616 MANUAL OF PHYSIOLOGY. 



sensation of pain can still be felt. A partial section of these 

 columns is followed by a local loss of touch in a part of the 

 skin of corresponding extent. This lesion is complete, as if the 

 impulses were transmitted directly by definite fibres in the cord 

 from each region of the skin. 5. Section of the an tero- lateral 

 white column causes loss of voluntary power in a corresponding 

 part of the same side of the body. If the gray matter be perfect, 

 the power of motion is soon restored, showing that the gray 

 matter can take on a function habitually performed by the medul- 

 lated fibres. The respiratory and vasomotor impulses appear to 

 be conveyed in the lateral white columns. 6. If the gray matter 

 and the posterior white columns be quite cut across, the impulses 

 giving rise in the brain to common sensation (pain), as well as 

 tactile impulses, are no longer carried to the centres, which shows 

 that the impulses causing common sensation travel exclusively in 

 the gray substance. 7. Section of one side of the gray matter 

 has, however, little effect. The passage of painful impressions is 

 not quite lost, even if both sides be cut at different regions of the 

 cord. The dullness of feeling is, moreover, general below the 

 injury; no one spot of skin being quite anaesthetic. A kind of 

 delay in transmission occurring from the " blocks," as if constant 

 decussation of the fibrils exists, but no direct or special channels 

 of communication. If the posterior white column be left intact, 

 the skin may transmit tactile impulses, but not painful ones. This 

 remarkable condition, called "analgesia," sometimes occurs in the 

 human being when partially under the influence of chloroform. 



THE SPINAL CORD AS A COLLECTION OF NERVE CENTRES. 



The various groups of cells in the spinal cord are in more or 

 less direct union with the roots of the nerves, and the conducting 

 fibrils of the cord itself, so that they participate in the transmis- 

 sion of the impulses to and from the centres situated in the brain. 

 In the transmission of these impulses, the cells seem to have a 

 certain directing and controlling influence which deserves special 

 attention, as it gives us the key to the more complex mechanisms 

 of the higher centres. Although the various powers exerted by 

 the cells of the spinal cord are so intimately associated together 



