354 PHYSIOLOGY 



ninised frog, however, it was only necessary to open the wound and 

 touch one of the divided posterior roots ^ to throw the whole body into 

 convulsions. As shown by Sherrington and Mott, division of all the 

 afferent nerves coming from the upper limb in monkey or man entirely 

 abolishes all contractions of the limb, which are usually effected 

 through the intermediation of the cerebral cortex. Cutting off the 

 major portion of the afferent impulses to the respiratory centre does 

 not, it is true, abolish all respiratory discharges, but converts the 

 rhythmic respirations into a series of inspiratory spasms which are 

 repeated at long intervals and are entirely inadequate for the proper 

 aeration of the blood. According to Sherrington a repetition on the 

 mammal of Hering's experiment does not lead to the same results, since 

 a spasmodic discharge is produced from the isolated spinal cord as a 

 result of asphyxia. But it is doubtful whether in this case there was 

 not some continuous excitation of the cord going on, as a result of the 

 closure of the demarcation current in the cut ends of the posterior roots 

 by the body fluids. It is possible that the neurons possess some 

 automatic power, i.e. some power of initiating nervous processes, 

 as a result of changes in the fluids surrounding them. This auto- 

 maticity, however, is not a prominent feature of the nervous system, 

 which has been evolved as a purely reactive mechanism to the 

 afferent impulses resulting from the material changes continually 

 taking place in the environment of the animal. 



