228 THE POPULAR SCIENCE MONTHLY. 



my subsequent argument will rest on the assumed correctness of three 

 postulates. The first of these is, that every manifestation of mind is 

 correlated to a definite mode and sphere of brain activity. This may be 

 emphatically insisted on, whatever be the view taken as to the nature 

 of mind itself. For, to take the illustration so frequently made use of 

 — that of the relation of a musician to his instrument— the volume and 

 quality and harmony of musical sounds are immediately correlated not 

 to the fingers of the player, but to the tremors within the instrument. 

 So the outcome of mental action, even as revealed to one's own con- 

 sciousness, is not simply the result of some ideal, self-acting energy 

 asserting itself, but it depends also on the compass and quality and 

 adjustment of a material organization. It, of course, follows, that if 

 we approach the subject from the physiological side, it is simply im- 

 possible to avoid the phraseology of materialism, and therefore, for 

 doing so, I shall make no further aj)ology. 



My next postulate is, that the activity of the brain is conditioned 

 by the activity of its circulation. The blood is to the gray matter of 

 the convolutions what atmospheric air is to burning fuel ; it is at once 

 a necessity and a stimulus. However favorable may be the arrange- 

 ment of cell and fiber, the consciousness will fail to respond to any 

 impression, and every cerebral function will be impaired or suspended, 

 if the circulation be lowered below a certain amount. 



It follows that, so far as physiological means are to enable us to 

 understand how mind and brain mutually act on one another, a con- 

 sideration of the laws that affect the distribution of blood, and the 

 influence of local surroundings in modifying these, must be of the first 

 importance. Yet this is what is very seldom attended to. Volumes 

 have been written on the relationship of mind and brain with scarcely 

 a single reference to this aspect of the subject. While considerable 

 progress has been made in defining the immediate sphere of activity, 

 in certain mental acts, and especially in mapping the centers for vol- 

 untary motion, very little attention has been given to the influence 

 wdrich the many peculiarities of the encephalic circulation must have 

 on the mode in which the brain may exercise its functions. 



The principal general fact in regard to the local distribution of 

 blood on which I have at present to lay stress is that, as a rule, the 

 supply to every tissue and organ is in proportion to the demand for it. 

 When function is quiescent, the need is slight in comparison with that 

 of active exercise, and accordingly w r e find that the circulation of any 

 organ contrasts remarkably in the two states. 



Considerable difference of opinion has existed as to how this is im- 

 mediately accomplished. By many writers the vaso-motor nerves seem 

 to be regarded as veritable physiological demons, whose unsleeping 

 vigilance foresees and provides for all local wants ; and it is supposed 

 that, while the whole motor force acting on the blood is supplied by 

 the heart's action, these nerves so regulate the caliber of the smaller 



