132 OF MIND. 



operating now on one part of the mechanism, now on 

 another, is the mind, the will, the thinking power itself. 

 What is the nature of this, and how does it act upon the 

 mechanism ? If the conclusions to which I have been led 

 with regard to the importance of germinal matter in all 

 ordinary nervous acts be correct, it is almost certain that 

 mental nervous action is very intimately associated with 

 changes occurring in a particular kind of living growing 

 matter. We find a large proportion of germinal matter 

 present in the grey matter of every kind of brain, and at 

 every period of life. Even in old age, when the proportion 

 of germinal matter in the various tissues and organs of the 

 body has become much reduced, a large amount is still 

 found in the grey matter of the brain. Moreover, the mental 

 excitement, wakefulness, and delirium, so remarkable in 

 many cases of fever and inflammation of the membranes 

 and superficial portion of the grey matter of the convo- 

 lutions, are invariably associated with changes in the 

 germinal matter. In such cases I find the masses of 

 germinal matter are much larger than in the healthy tissue, 

 and, in some instances they are twice as large. I have also 

 seen the enlarged mass in the centre of the caudate nerve- 

 cells dividing into several masses which resemble pus 

 corpuscles, and have the same appearance as the pus 

 corpuscles which are sometimes seen in epithelium 

 (PL VIIL, p. 34). 



But if it be admitted that mental phenomena are entirely 

 due to changes in the germinal matter of the cerebral con- 

 volutions, there will be much difference of opinion con- 

 cerning j.th^. precise way in which this germinal matter 



S A 



