GROWTH OF THE CORPUS CALLOSUM 43 



2. Concerning myelination in the callosum, we have noted 

 "i;he following: A small number of scattered myelinated fibers is 



found at the tenth day after birth. This number increases 

 gradually till the twenty-fifth to twenty-seventh day, at which 

 age the myelinated fibers are evenly distributed over the entire 

 section. 



After this period the myelinated callosal fibers grow mainly 

 in size rather than in number up to at least the 378th day. 

 Thus the great increase of the callosal area, which takes place 

 after the tenth day, appears to be due for the most part to 

 the increase in the diameter of the fibers combined with the 

 formation of new myelin sheaths. 



3. As shown by Koch ('17, table 3), the callosum exhibits the 

 chemical changes characteristic for white matter, and thus 

 during growth it shows a rapid and large increase in lipoids and 

 a corresponding decrease in its water content. 



4. According to Koch ('17), the corpus callosum of the human 

 brain loses from 18 per cent to 20 per cent of water, while, owing 

 to the slight admixture of myelinated fibers, the gray matter 

 loses only from 2 to 5 per cent of water from birth to maturity. 

 These changes in the water content, which are associated with 

 the change in the lipoid content, are much greater, therefore, in 

 the corpus callosum than in the cortex, in which the changes 

 are only shght. 



h. Comparison between the growth of the callosal area and of the 



total brain area 



From the brain weights on the observed body weight (calcu- 

 lated from the formula Br. W. = 0.554 + 0.569 log (body 

 weight — 8.7) as are given in column B and C, table 2, we can 

 express the area of the total brain, considered as a cube, by the 

 values for the square of the cube root of the brain weight. In 

 this treatment the variations in the specific gravity of the brain 

 have been neglected. In chart 1, B, the upper curve represents 

 the area (reduced) of the total brain, on body weight, the actual 

 values of the ordinates being reduced by multiplying by the 



