Philosophical Conceptions of Life. 259 
other tissues, they would be accompanied by an increased ex- 
cretion of characteristic waste-products, by evolution of heat 
and by afflux of blood. Experimental investigation has been 
directed to each of these points, and some important observa- 
tions have no doubt been made; but much of the testimony 
is conflicting, and our knowledge is still so incomplete that 
further inquiry in each direction is greatly to be desired. 
This is particularly the case with regard to the chemical 
questions connected with the metabolism of the brain. In 
the first place, our knowledge of the chemical composition of 
brain-substance is still in its infancy. The view that its 
characteristic ingredient is the phosphorized nitrogenous body 
described in 1865 by Liebreich under the name of protagon 
has been strongly controverted by Diaconow, Hoppe-Seyler, 
and Thudicum, while recently it has been reaffirmed by 
Gamgee and Blakenhorn*. But even should this view turn out 
to be well founded, we have yet every thing to learn with regard 
to the transformations protagon undergoes during functional 
activity, and the nature of the resulting waste products. 
Long before Liebreich announced the existence of protagon, 
however, the attention of the physiological chemists had been 
directed to the prominence of phosphorus as an element in 
the composition of the cerebral substance, and it had been 
suggested that a part of the phosphoric acid excreted in the 
urine might be derived from the metabolism of the brain. As 
early as 1846 Bence Jones} had observed an excess of phos- 
phatic salts in the urine during certain brain-diseases, notably 
acute inflammations ; and an observation published in 1853 
by Mosler} appeared to indicate that a similar excess followed 
intellectual activity. 
Byasson [1868] in his essay on the relation between cere- 
bral activity and the composition of the urime§, reports a 
number of urinary analyses which support the view that the 
excretion of alkaline phosphates by the kidneys is habitually 
increased during mental work. ‘This opinion has also received 
a certain degree of support from the more recent papers of 
Ziilzer || and Stribling{[; nevertheless it is impossible to 
* Gamgee, p. 425 et seg. op. cit. supra. 
+ Henry Bence Jones, “ On the Variations in the Alkaline and Harthy 
Phosphates in Disease,” Phil. Trans. for 1846, p. 449. 
t Mosler, “ Beitrige zur Kenntniss der Urinabsonderung,” &c., Inaug. 
Diss., cited in Canstatt’s Jahresbericht, 1853, Bd. i. 8. 154. 
§ H. Byasson, “Essai sur la relation qui existe a l'état physiologique 
entre activité cérébrale et la composition des urines,” Paris, 1868. 
|| W. Ziilzer, “ Ueber das Verhiiltniss der Phosphorsiure zum Stick- 
stoff im Urin,” Virchow’s Archiy, Bd. lxvi. 1876, 8. 228. 
{| Striibling, “ Ueber die Phosphorsiiure im Urin,’ Archiv fur exp, 
Path. und Pharm., Bd. vi. 1876-77, 8. 266. 
