116 



ANATOMY 



Myelin formation. Using the data in table 74 (Donaldson 

 '15, "The Rat") Sugita ('17) has computed the weight of the 

 dry substance in the brain of the Albino according to brain 

 weight. The relations found are given in the solid graph in 

 chart 13. As this shows, a period of relatively rapid increase 

 in the solids occurs when the brain weight of 0.95 grams is 

 reached and continues up to about 1.35 grams. These brain 

 weights correspond to 11 and 33 days respectively. When a 



Chart 13 The dotted line shows the ratio between the initial brain weight 

 and the weight after its dehydration and extraction in 80 per cent alcohol (for 

 twenty-four hours) and 90 per cent alcohol (for twenty-four hours) according to 

 a uniform procedure, plotted on the brain weight. The data were taken from 

 table 79. The graph was drawn connecting the middle points of each pair of 

 entries. X and XX indicate the turning points in the graph. 



The solid line shows the absolute weight of the solids in the brain according 

 to the brain weight. The data were taken from table 74 in 'The Rat' (Donald- 

 son, '15) and calculated by me. * and ** indicate the turning points in the 

 graph. 



For the ratios of brain weight the scale is given on the left side of the chart 

 and for the absolute weight of the solids the scale is given on the right side. 



series of albino brains of different ages are extracted with 80 

 per cent alcohol for 24 hours, followed by 90 per cent alcohol for 

 24 hours, and the moist brain weight after treatment in deter- 



