58 SHINKISHI HATAI 
lination is completed in the fish brain relatively earlier than in 
the mammalian brain. 
3. With respect to the total nitrogen, nitrogen in ether-alco- 
hol extract, and the lipoid content, the fish brain closely resembles 
the stem of the rat brain, but significantly differs from the entire 
rat brain. This is explained by the fact that the mature fish 
brain resembles essentially the stem of the mammalian brain 
owing to the small growth of cerebrum and cerebellum. 
4. The non-protein nitrogen is considerably greater (42 per 
cent) in amount in the fish brain than in the rat brain. The 
suggestions were made that probably on account of unstable 
physical consistence of the fish nervous system, the wear and tear 
of the neurons may be greater than in the more highly organized 
mammalian nervous system, thus producing a larger quantity 
of the waste products, and also that on account of higher non- 
protein nitrogen content of the fish blood, accompanied by a 
slow circulation, the deposition of the waste products might 
become greater, and at the same time a less vigorous removal 
further tends to increase the accumulation. . 
5. The greater fraction of the non-protein nitrogen is repre- 
sented by the amino acid nitrogen in both the fish and the-rat. 
6. The amounts of urea nitrogen and of ammonia nitrogen 
are closely similar to those found in the rat brain, 
