METABOLIC ACTIVITY OF NERVOUS SYSTEM 57 
2. According to Folin and Denis (’14) the normal human blood 
contains, on the average of four cases, 32 milligrams of non- 
protein nitrogen per 100 ce. of blood, while Wilson and Adolph 
(17) found in the blood of various fresh water fish much higher 
values for the non-protein nitrogen (42 mgms. per 100 ec.) than 
in the human blood, and furthermore these investigators found 
a greater fraction of the non-protein nitrogen was represented 
by the nitrogen of amino acids (23 mgms. per 100 ce. or about 
55 per cent of the total non-protein nitrogen). Thus my own 
observations on the fish brain closely agree with those of Wilson 
and Adolph on the fish blood, so far as the relative abundance 
of the non-protein nitrogen is concerned, as well as in the relation 
of the amino acid nitrogen to the total non-protein nitrogen. 
Denis (?13—14) found also a considerably greater amount of 
non-protein nitrogen in the blood of marine fishes when con- 
trasted with human blood. Denis found 62 mgms. of non-pro- 
tein nitrogen per 100 ce. of blood (average of 10 species of teleosts) 
and as high as 1087 mgms. in the case of the elasmobranchs 
(average of three species). Thus the greater abundance of the 
non-protein nitrogen in the fish blood, accompanied by a slow 
circulation, might be largely responsible for a greater accumu- 
lation of the non-protein nitrogenous extractive substances in 
the fish brain. 
SUMMARY 
The gray snapper, Neomaenis griseus, was mainly used for 
the present investigation. The following are the more impor- 
tant facts brought out. 
1. The relation between brain weight and body length is prac- 
tically linear. This linear relation appears in the fish as small 
as 150 mm. in length. The fish smaller than 150 mm. were not 
studied because they could not be obtained. 
2. The percentage of water in the brain varies very little from 
small to large (body length : 88 mm. to 448 mm.). <A similar 
relation was observed by Donaldson (’05) in the brain of the 
summer flounder and by Scott (712) in the brain of the smooth 
dogfish. The probable explanation is that the process of mye- 
