COMPOSITION OF BRAIN OF ATAXIC PIGEONS 103 



ences in the whole brain of the two most strongly affected groups, 

 two or three fractions indicate equivalent age, two indicate older 

 age, and thirteen fractions indicate younger age than was actu- 

 ally theirs. It is difficult to believe that such results would have 

 been obtained on two groups of brains not actually unlike in de- 

 gree of chemical differentiation. Similar differences in smaller 

 degree and of less definiteness occur in the one strongly ataxic 

 cerebrum and cerebellum-medulla group analyzed. The whole 

 brains of two additional groups of birds showing relatively little 

 ataxia gave nearly indifferent figures in respect to age. It seems 

 necessary to conclude that the result of the two series of brain 

 analyses indicates that chemical differentiation does not proceed 

 as rapidly in the brain, perhaps more particularly in the cerebel- 

 lum-medulla of ataxic birds as in the brain of normal birds. 

 Moreover, chemical under-differentiation of the ataxic brain 

 certainly maj r persist into very mature age. 



DISCUSSION 



Analyses and materials 



In our analyses we have been obliged to deal with groups of 

 brains and not with individual brains. This fact has a bearing 

 on the results obtained. The ages of some of the birds of an 

 older group were not very dissimilar to that of some of the birds 

 placed in a younger group. The material entering into the sam- 

 ples is further complicated by the possibility that some among 

 the birds considered as normal might later have shown obvious 

 ataxia. The ataxia manifests itself in various degrees and be- 

 comes evident at various ages. Ataxia exhibited in early life 

 may later wholly disappear. Some of the ataxics selected may 

 have been well under way to recovery. It seems probable that 

 the observed differences in chemical composition between ataxic 

 and normal brains would have been greater if it had been possible 

 to analyze single brains instead of groups of brains. In connec- 

 tion with these remarks, we would ask that it be borne in mind 

 that unlimited numbers of ataxic birds have not been available 

 to us, since the derangement, though hereditary, behaves rather 

 as a recessive than as a dominant (Riddle, '18). 



