44 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



Ewald were able to show that the same phenomena 

 may also be observed when the hind-legs of dogs 

 whose spinal cord has been destroyed are packed for 

 a time in snow. 



From the standpoint of human physiology these 

 results seem strange, but from that of comparative 

 physiology they are readily understood. The various 

 reactions of plants to external stimuli are just as pur- 

 poseful as those of animals. Why should it not be 

 possible, then, for single organs and tissues of higher 

 animals to react purposefully to external stimuli, and 

 is there any reason why the purposeful character of a 

 reaction should be dependent upon the structure of 

 the central nervous system ? 



We have been able to rid ourselves of erroneous 

 views concerning the significance of the ganglia of 

 the central nervous system in higher animals through 

 the help of the Ascidians ; they also help us further to 

 determine the true role of the nervous system. Al- 

 though the dogs experimented upon by Goltz and 

 Ewald were able to adapt the width of their blood- 

 vessels to the variations of temperature, it was neces- 

 sary to shield them much more carefully from sudden 

 changes of temperature than is necessary in the case 

 of normal animals. The threshold of stimulation was 

 raised and probably the rapidity of the conduction 

 decreased. For this reason, dogs whose spinal cord 

 is destroyed are no longer fit to live out-of-doors. 

 As regards regulation of temperature, they are like 

 an intoxicated person, and would perish in the cold 



