268 PHYSIOLOGY FOR DENTAL STUDENTS. 



travel through the brain (p. 248), many nerve centers become 

 more or less involved in the reflex actions, so that a much higher 

 degree of co-ordination than that seen in a spinal animal attends 

 the muscular response. For example, some of these afferent 

 impulses reach the cerebellum, whose function, as we shall 

 is to strengthen some impulses and weaken others, so that a 

 more perfect movement results. 



4. The animal becomes conscious not only of the nature and 

 place of application of the sensory stimulus itself, but of the 

 degree to which it has moved its muscles in response. 



The Functions of the Cerebrum. 



The complicated movements, such as those involved in the 

 scratch reflex, which we have seen that a spinal animal can carry 

 out in the paralyzed region after shock has passed away, become 

 more and more numerous and complicated as the higher centers 

 are left in connection with the spinal cord. That is to say, the 

 higher up in the cerebrospinal axis that the section is made, the 

 more capable does the part of the animal below the section be- 

 come to peform complicated movements. The important centers 

 in the medulla, pons and mesencephalon add their influence to 

 those of the spinal cord itself, so that integration becomes more 

 comprehensive. If the cut is made above the level of the pons. 

 in other words, if the cerebral hemispheres alone be discon- 

 nected from the rest of the cerebrospinal axis f/rrm hr<ifiun, 

 as it is called we obtain an animal possessing all the reflex 

 actions that are necessary for its bare existence, although it is 

 of course incapable of feeling or, if the basal ganglion be also 

 destroyed, of seeing or hearing. It becomes a mere automaton: 

 it breathes, the blood circulation is normal, it can walk or run 

 or swim, it swallows food if the reflex act of swallowing be 

 stimulated by placing the food in the mouth, but it has not the 

 sense to take food itself .even when this is placed near it. All 

 the mental processes are absent; it has no memory, no volition, 

 no likes and dislikes. By seeing that it takes food, it has been 

 possible to keep such a decerebrated dog alive for eighteen 

 mouths, and the lower we descend in the animal scale, the easier 



