CHAPTER XXIII 



PHYSIOLOGY OF THE BRAIN-STEM 



1. GENERAL SURVEY 



WE have seen in the previous chapter that the spinal cord exercises con- 

 trol over many different functions of the body. We have now to learn that 

 an even more complete control is exercised by the highest parts of the central 

 nervous system, namely, the parts lodged in the cranium and which, taken 

 collectively, we call the brain. For, as we shall see later, it is no difficult 

 matter to demonstrate that even the cerebral cortex, the highest part of all, 

 can exert its influence over functions which are quite independent of the will. 

 Experiment has shown that this influence varies with different divisions of 

 the brain, and that from the standpoint of the different functions we must 

 for this reason ascribe to the different parts a dignity of a very different order. 

 For the purely vegetative functions, especially those which have most to do 

 with the mere maintenance of life, like the circulation, respiration, digestion, 

 etc., the lower parts of the brain, particularly the medulla, are the most im- 

 portant ; while the cerebrum is for very good reasons regarded as the material 

 substratum of the conscious processes. 



The extremely varied functions of the brain make it necessary that the 

 nervous pathways should be connected with each other in manifold ways, and 

 accordingly we find the structure of the brain extraordinarily complex. This 

 circumstance is, for the physiological and clinical as well as for the anatomical 

 mode of attack, the source of very great difficulties, which so far have been 

 only very imperfectly surmounted. Our knowledge of the functions of the 

 brain as a whole and of its different parts is therefore very inadequate, and 

 the data which we have are unfortunately very contradictory as to many of 

 the most important points. 



A. METHOD 



The methods which can be employed in investigating the functions of the 

 brain are in general similar to those with which we have already become familiar 

 in the study of the spinal cord : anatomical study of its structure, artificial stimu- 

 lation, section or removal of different parts, clinical observations on patients 

 followed by post-mortem dissection, etc. But, as will be readily understood, the 

 practical difficulties to be overcome here are very much greater than those met 

 with in the study of the cord. Not only is the danger of disturbance to the cir- 

 culation, caused by section or removal of a part, as well as the shock produced 

 by the operation, greater in dealing with the brain, so that effects are very often 

 much exaggerated at first, but in many cases the function lost is assumed by 



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