20 
PHYSIOLOGY: S. HATAI 
snapper. This difference may be due to the fact that in the dogfish the brain 
possesses a voluminous cerebellum, as well as olfactory bulbs, and the com- 
bined weights of these two structures being greater than that of the rest of 
the brain, while these two structures in the gray snapper are very small. It 
appears that these two parts, olfactory bulbs and cerebellum of the dogfish 
brain, grow very rapidly during the earlier period, thus giving a form of the 
graph similar to that of the mammal. 
2. Percentage of Water in the Brain. — Altogether 64 snappers were examined. 
It was found that so far as the present data are concerned, the percentage of 
water in the small and large fish is nearly identical within a wide range of 
body length, and therefore the percentage of water does not vary regularly with 
the length or size of the fish. Similar relations were observed by Donaldson 3 
in the brain of the summer flounder and by Scott 4 in the brain of the smooth 
dogfish. 
It is also interesting to note that the average percentages of water obtained 
by Donaldson, Scott and myself are nearly the same, being 78.4% (flounder), 
78.5% (dogfish) and 78.61% (gray snapper) respectively. It is worthy of 
note that the values given by these fish are not much different from (slightly 
above) the percentage of water in the adult mammalian brain. 
Since the reduction of the water in the brain is induced by the deposition of 
the 'myelin substance' 5 we may infer that the process of myelination in the 
fish brain occurs at a very early period, thus producing slight variation from I 
small to large individuals, as here recorded. I have not however been able 
to determine the period of rapid reduction of the water content in the brain 
which must take place in this fish in consequence of the appearance of myelin, 
because of lack of very young material. 
3. Chemical Analysis of the Brain. — Altogether 51 dried brains as well as 44 
fresh brains were used for the purpose of the chemical analysis. With respect 
to the nitrogen in total solids, nitrogen in ether-alcohol extract, and the lipoid 
content, the fish brain closely resembles the stem of the rat brain, but signifi- 
cantly differs from the entire rat brain. This is explained by the fact that the 
fish brain corresponds essentially to the stem of the mammalian brain, owing 
to the small growth of the cerebrum and cerebellum. The content of non- 
protein nitrogen is considerably greater in the fish than in the rat brain. This 
phenomenon is interesting and I wish to call attention to two factors which 
may have some bearing on it. 
It seems probable that on account of the low grade of organization of the 
fish brain, the physical consistence of the nervous system may not be as stable 
as that of more highly organized mammalian nervous systems, and thus the 
wear and tear process may be much greater, producing a correspondingly 
greater amount of waste products in the fish brain. 
Again it has been found by several investigators that fish blood contains a 
greater abundance of non-protein nitrogen compared with human blood. The 
content of non-protein nitrogen in the rat blood is nearly identical with that 
