94 MATHILDE L. KOCH AND OSCAR RIDDLE 



phosphatids) which are really indicative of age in very young 

 brains have very limited or quite uncertain values when applied 

 to brains of some of the older ages. This particularly applies to 

 several ages actually studied by us. It is, therefore, necessary to 

 restate here the chemical criteria for differentiating younger and 

 older stages, as this applies to the pigeon brain for those particu- 

 lar ages which we are now to compare. 



The data given in table 8 require the following conclusions : 



Water is decreased relative to solids throughout the entire age 

 series. It is true that the moisture figures obtained for the sev- 

 eral groups of normals do not correctly indicate the age of the 

 group in all cases. For example, the normal brain of 106 days 

 is shown to have a slightly lower percentage of water than the 

 normal brains of 205 days, and an ataxic of 133 days slightly less 

 water than an ataxic of 206 days. Ataxia itself probably further 

 complicates the smoothness of the figures for the series as a 

 whole. Nevertheless, a general tendency to a decrease of water 

 with increasing age is unquestionable. 8 



Protein plainly decreases with increased age. Only the figure 

 for the normals of 106 days breaks the complete smoothness of 

 the curve for the entire series of normals. 



Lipoids increase with increased age, although the figures actu- 

 ally obtained are not wholly consistent, neither for the normals 

 considered alone nor for the ataxic series. In fact, between 106 

 days and 598 days very little change is indicated in the amount 

 of lipoids. This doubtless indicates that myelination is prac- 

 tically completed in these pigeons at 106 days. 



Extractives are present in the solids in greater amount in the 

 forty-five day brain than at any other time. In normals of 106 

 days, however, no more extractives are present than in normals 

 of 2,021 days, and less is found than in normals of 205 and 598 



8 It should be borne in mind that there is opportunity for error in the moisture 

 estimation of any organ such as the brain. First, through unequal evaporation 

 from the brain surface during the preparation of the sample, and, second, through 

 the presence of unequal quantities of blood within the organ when weighed. 

 Whether ataxia itself offers any special complication is at present unknown to us. 

 Again, any loss or gain to the solids of either the alcohol-ether soluble or alcohol- 

 ether insoluble fraction would serve to modify the recorded amount of moisture. 



