NERVOUS SYSTEM 



117 



mined, Sugita ('18) finds a progressive loss in weight with ad- 

 vancing age as indicated by the ratio to the initial brain weight 

 ■ — table 79, chart 13. These data show that the period of most 

 rapid extraction approximately coincides with the period of 



TABLE 79 

 Giving for each brain-weight group of the normal albino rat the average initial 

 brain-weight in the fresh condition and the brain weight after dehydration and 

 extraction in 80 per cent alcohol (for twenty-four hours) and 90 per cent (for twenty- 

 four hours) by a uniform procedure. The ratio of the final brain weight to the 

 initial weight is given in the last column as a percentage value. Based on ob- 

 servation on 120 albino rats, sexes combined. 



most rapid increase in solids. As the substances extracted 

 are largely the alcohol soluble lipoids, such as appear in the 

 myelin sheaths, it is inferred that the interval between 11 and 

 33 days is one in which a rapid formation of the myelin sheaths 

 occurs in the brain. 



In his studies on myelination in the nervous system of the 

 rat, Watson ('03) found the first evidence of myelin formation 



