NERVOUS SYSTEM 139 



Chart 16 shows the relations found. Two hours after feeding 

 the amount of non-protein nitrogen in the brain is high. This 

 amount diminishes almost steadily up to nine hours after feeding. 

 It then increases up to twenty-four hours, returning to the value 

 in the control. The relations for the percentage of non-protein 

 nitrogen on total nitrogen are similar, and the differences in the 

 percentage of water in the brain follow a like course. 



The excitement of fighting and of electrical stimulation causes 

 an increase in the content of non-protein nitrogen in the brain, 

 Komine ('19 a). 



Spinal cord. See References. 



(6) Peripheral : Degeneration, Regeneration. Nittono ('23) re- 

 ports that when the second and third branches of the trigeminus 

 nerve are sectioned, retrogressive changes appear in the fibers 

 after one day, and in the small cells of the ganglion between the 

 first and second day. The degenerative processes are at their 

 height from the 5th to the 20th day. Regenerating fibers are 

 seen from the third to the fifth day on. Residual evidences of 

 degeneration may be detected as late as 60 days after the opera- 

 tion. Similar responses, but less intense, occur on the intact side. 

 For numerical data in the regenerating n. peroneus see Green- 

 man ('13.) 



4. Special senses. The correlation between structure and 

 function in the development of the special senses of the white 

 (albino) rat has been studied by Lane ('17). 



Touch : Reactions. Pricking with a needle, fetuses 16 mm. 

 (crown-rump measurements) on flank, sides and snout produces 

 slight but perceptible movements. At birth the rat responds to 

 touch of a brush by contortion of the body limb movements 

 and squeaks. 



Structural conditions. In 16 mm. fetuses about a dozen anlagen 

 of vibrissae are present in the snout. A reticulum formed by a few 

 nerve fibers at the base of each vibrissa is seen. At birth there 

 are more vibrissae, more fibers to each of them, more tactile 

 fibers to skin. 



Equilibrium : Reactions. In a fetus of 35 mm. the first indica- 

 tion of equilibrium sense appears. The rat maintains an upright 

 position. At one day of age the rat makes awkward efforts to 



