VARIATIONS IN THE URINE. 231 



very interesting work upon the influence of cerebral activity 

 upon the composition of the urine, by Byasson, they have 

 been somewhat extended. Byasson found that by mental 

 exertion the quantity of urine was increased ; the amount 

 of urea was also increased; the phosphoric acid was in- 

 creased about one-third ; the sulphuric acid was more than 

 doubled ; and the chlorine was nearly doubled. 1 



These facts have an important bearing upon our knowl- 

 edge of the effects of mental exertion upon the process of 

 disassimilation of the nervous tissue. They show that nearly 

 all of the solid principles contained in the urine are in- 

 creased in quantity by prolonged intellectual exertion, but 

 they fail to point to any one excrementitious principle, either 

 organic or inorganic, which is specially connected with the 

 physiological wear of the brain. It has been assumed that 

 elimination of the phosphates, increased out of proportion 

 to the increase of the other solid matters of the urine, is one 

 of the constant effects of intellectual effort ; but this view 

 is not sustained by direct physiological experiments, nor by 

 facts in pathology. We have already discussed this question 

 somewhat elaborately, under the head of the phosphates of 

 the urine. 8 



1 BYASSOX, Essai sur la relation qui existe d fetal physiologique entre Vactivite 

 c'er'dbrale et la composition des urines, Paris, 1868, p. 48, Table. 

 8 See p. 215. 



