THE BEGINNINGS OF LIFE. 41 



and M. Byasson think that such evolution of heat is 

 produced by an increased amount of chemical change 

 in the active parts; though the investigations of Dr. 

 L. H. Wood 1 go to show that (as was the case in the 

 activity of muscle) the liberated energy is not derived 

 from the oxidation of the nerve-substance itself, but 

 rather from an oxidation of the pabulum supplied by 

 the blood to the functionally active parts. It is quite 

 reasonable to suppose, however., that nerve-organs, by 

 virtue of their activity, should undergo a certain amount 

 of waste 2 ; and, probably, it is this of which we get 

 evidence in the observations of Liebreich as to the 

 diminution of protagon in parts of the nervous system 

 which had long been in a state of uninterrupted activity. 



doubt on this subject then the local increase of heat may be due to 

 mere increased afflux of blood, either alone or supplemented by heat 

 which is liberated during the molecular changes taking place in the 

 nerve-tissue itself, 



1 ' On the Influence of Mental Activity on the Excretion of Phos- 

 phoric Acid by the Kidneys.' (' Proceedings of Connecticut Medical 

 Society,' 1869, p. 197.) 



2 The researches of Professor Haughton (' Dublin Quarterly Journal 

 of Medical Science,' 1860) and also of M. Byasson (' Thfese de Paris,' 

 1868, No. 162) have shown that the same individual during periods in 

 which he has undergone much intellectual labour and a minimum of 

 muscular exercise, passes as much or even more urea than during other 

 similar periods when there has been much muscular exertion and a 

 minimum of intellectual labour. The analyses of M. Byasson go to 

 show that the same individual, under the influence of the same diet, 

 passed in 24 hours the following quantities of urea : 



During a period of rest 20-46 grms. 



During a period of muscular labour .... 22-90 

 During a period of cerebral activity .... 23-88 ,, 



