Gradation of the Veriehraia. 149 



10//;. Density. 



The actual amount of nervous matter is to be regarded 

 rather than the space it occupies. Some ganglia are hollow in 

 one order and solid in another. Errors are liable to arise from 

 this. Again the structure where solid may be more dense in 

 one case than in another. The specific gravity will be a valu- 

 able guide. Simple weight will not answer. A dense struct- 

 ure will unquestionably differ in functional power from a loose 

 one of equal weight. 



lltJi. Quality of the nervous organization. 



This, unquestionably, it is difficult to determine with cer- 

 tainty and precision, but its significance cannot be questioned. 

 It is a very important element in determining superiority 

 among men, where it can be estimated somewhat accurately, 

 and it is doubtless equally so among the whole class vertebrata. 

 A general harmony of structure pervades the organization of an 

 animal. Coarseness in one part is usually accompanied by 

 coarseness in all others, and vice versa. It is not difficult to 

 determine the general quality of the organization as a whole, 

 and thus we may form a general though somewhat uncertain 

 estimate of the quality of the nervous organization. What 

 assistance microscopic study may lend in this estimate is not 

 yet demonstrated. That it will be important, it is reasonable 

 to hope. 



12th. Activity of the nervous system. 



Like quality, this may be difficult to determine, but yet 

 it is important. Yet I think, in the amount and in the changes 

 of the blood sent to the brain, we have a reliable index of its 

 activity. I am not aware that any observations, save a few 

 by the author, have been made with this end in view. Yet 

 the value of such observations are apparent upon a mere state- 

 ment. And that value is not confined to the determination of 

 activity merely, but of the total amount of nervous force. The 

 K. 



