446 



H. H. DONALDSON 



say tlio lii)oicl uiul the non-lipoid fractions. The lipoid (in 

 part) represents the myeUn sheaths, while the protein, with the 

 remainder of the lipoid, represents the cell bodies and their 

 unsheathed axons. 



With the exception of the one day group, the ages for which 

 analyses were made, are given in table 2. 



TABLE 2 

 To show, fur Ihc brain of the albino rat at five ages and for the spinal cord at one 

 age the percentage of water in the myelin as computed according to the method 

 described. The protein and lipoid are given in percentages of the total dry sub- 

 stance. (Based on table 2. Koch and Koch '13) 



Brain 



Spinal cord 



120 



52.92 



47.08 



4.2 



70.4 



87 



51.0 



1 First traces of myelin. 

 - Myelin well shown. 



At one day — or practically birth — it is found that the lipoid 

 is present to the extent of 0,31 or nearly one-third of the weight 

 of the protein. There is, however, no visible myelin at this age, 

 so it is concluded that this proportion of the total lipoid is nor- 

 mally associated with the protein and is not to be included in the 

 lipoid which forms the myelin sheaths. We have treated the 

 data for the later age groups in accordance with this relation, 

 and in each case have taken from the total lipoid found an 



