414 COSMIC PHTLOSOPHY. [ft. ii. 



of conscious changes, which is implied in elaborate quanti- 

 tative reasoning, cannot go on at all. Now the need for the 

 constant presence of nutritive material is a meaningless fact 

 unless each change in consciousness is dependent upon a 

 molecular transfer between the nutritive material and the 

 nerve-substance. 



Thirdly, the maintenance of conscious changes requires 

 the presence of certain particular materials in the blood, 

 and the absence, in any save the smallest proportions, of 

 certain other materials ; while there are yet other materials 

 upon the presence of which the rate and complication of 

 conscious changes largely depend. The familiar fact that 

 consciousness cannot for an instant continue unless oxygen 

 is in contact with the grey tissue of the cerebrum, is alone 

 sufficient to prove that no conscious change is possible, save 

 as the accompaniment of a chemical change. On the other 

 hand, the presence of carbonic acid or of urea in consider- 

 able quantities retards the rate and prevents the elaboration 

 of thinking ; and in still larger quantities it puts an end to 

 consciousness. And in similar wise the effects of alcohol, 

 opium, and hemp, as well as of that Siberian fungus whose 

 inhaled vapour makes a straw in the pathway look too large 

 to be jumped over, show us most vividly how immediate is 

 the dependence of complex mental operations upon chemical 

 changes. 



Fourthly, the fact that the vigour and complexity of 

 mental manifestations bear a marked ratio to the weight 

 of the brain, to the amount of phosphorus contained in its 

 tissue, and to the number and intricacy of the fine sinuous 

 creases in the grey surface of the hemispheres, shows plainly 

 that changes in consciousness are conditioned both by the 

 amount and by the arrangement of nerve-material. 



Fifthly, we may see a like significance in the facts that 

 the amount of alkaline phosphates excreted by the kidneys* 

 varies with the amount of mental exertion ; and that emo- 



