COMPOSITION OF BRAIN OF ATAXIC PIGEONS 99 



difference which is consistently interpreted on the basis of age. 

 The differences found, however, favor the view that both the 

 cerebrum and cerebellum-medulla of the ataxics were somewhat 

 younger than the normals with which they are compared. In 

 reality, our observed moisture differences of 0.1 per cent are 

 insignificant. 



The cerebrum of the older (strongly) ataxic group show de- 

 creased water, lipoids, cholesterol (phosphatids, sulphatids), 

 lipoid-sulphur, lipoid-phosphorus, and total phosphorus, when 

 compared with the amounts found in the older normal group. 

 Increased values are shown for protein (extractives) , protein phos- 

 phorus and extractive-phosphorus. Seven of these figures indi- 

 cate juvenility or chemical under-differentiation of the ataxics 

 as compared with the normals of equivalent age. Two figures, 

 those for the very nearly equivalent water and total phosphorus, 

 oppose this interpretation. Reference to table 4 will show that 

 the cerebrum in this group of ataxics was below normal size. 



The cerebellum-medulla of the older ataxics show decreased 

 amounts of water, lipoids (extractives), cholesterol, lipoid-phos- 

 phorus, and extractive-phosphorus, and increased amounts of 

 protein (phosphatids, sulphatids), lipoid-sulphur, protein-phos- 

 phorus, and total phosphorus. Of these figures, six are in favor 

 of, and three are opposed to, the view that the cerebellum- 

 medulla of the ataxic group is more juvenile than that of the 

 normal group.. 



Most of the chemical evidence which is distinctive of age indi- 

 cates, therefore, that both parts of the brain of the older group 

 of strongly ataxic birds (600 days) were somewhat less old than 

 the older normal brains (598 days) with which they must be com- 

 pared. Similar evidence was found for both cerebrum and 

 cerebellum-medulla of the younger (less) ataxic group. 



Concerning the whole of the new evidence obtained by a com- 

 parison of the chemical composition of the parts of the brain of 

 normals and ataxics, it can be said that all of the four tests made, 

 support the interpretation which was given to our previous re- 

 sults. Most of the evidence indicates that the cerebrum and 

 cerebellum-medulla of both ataxic groups are chemically less dif- 



