COMPOSITION OF BRAIN OF ATAXIC PIGEONS 109 



SUMMARY 



1. The brains of birds which have lost a very large amount of 

 the normal control of the voluntary movements (ataxia) show 

 deviations from the normal brain in size and in chemical compo- 

 sition. These deviations are more pronounced in the cerebellum- 

 medulla. 



2. The brains of the ataxics are smaller. The cerebrum is 

 either not reduced or is reduced in very small amount. The cere- 

 bellum-medulla (weighed together) is certainly reduced in size. 



3. Possibly the somewhat smaller brain size of the (mature) 

 ataxics is necessarily associated with a relatively less amount of 

 white substance. If this is true, some, but not all, of the ob- 

 served inequalities in chemical composition may be associated 

 with this circumstance. The whole of the results would never- 

 theless emphasize the existence of some retarding influence on the 

 completion of growth in the ataxic brain. 



4. Eight analyses were made of anterior and posterior parts 

 of the brain. Four of these were from ataxic birds and four 

 from normal birds. The chemical changes found are more defi- 

 nite and pronounced in the cerebellum-medulla than in the cere- 

 brum. The results support our previous conclusion that the 

 differences "suggest a chemical under-differentiation or imma- 

 turity of the ataxic brains." 



5. The pigeon cerebrum and cerebellum-medulla strongly con- 

 trast with the human cerebrum and cerebellum-medulla in the 

 distribution of the several chemical constituents. 



6. Entire brains of very young and of very old birds were 

 analyzed. Data for the chemical changes in the brain which 

 accompany age have been obtained for a scries of ages in the 

 pigeon. Examination of this more extensive 'age series' of pigeon 

 brains has enabled us to evaluate much better than in our previ- 

 ous work the relation borne by the various chemical fractions to 

 age and has also drawn attention to the relatively greater abso- 

 lute brain weight in the males and the relatively greater weight 

 of the cerebellum-medulla as compared with the cerebrum in the 

 females. 



