COMPOSITION OF BRAIN OF ATAXIC PIGEONS 95 



days. The smallest percentage of extractives was found in nor- 

 mals of 183 days. It is therefore clear that in brains older than 

 106 days the variations in amount of extractives noted by us 

 have a wholly doubtful significance with respect to age. 



Cholesterol steadily increases with age. The relative age of all 

 except one of the normal groups is correctly expressed by the 

 amount of cholesterol found. 



Phosphatids increase with age (total phosphorus, in per cent of 

 solids, steadily decreases with age) until about 205 days. The 

 amount then decreases slightly. It is probable that low phos- 

 phatids, as in birds of 600 days, 9 is indicative of relative imma- 

 turity, since it is only in very immature brains that low phospha- 

 tids are normally found. The highest figure obtained was for a 

 group of 183 days. 10 In general, therefore, phosphatids cannot 

 be considered distinctive of age in brains older than 183 days. 



Sulphatids certainly increase with increased age (total sulphur, 

 in per cent of solids, fluctuates with age) to 205 days or more; 

 but the figures obtained, like those for phosphatids, are not en- 

 tirely consistent. The highest figure for sulphatids was obtained 

 in brains of 205 days. It seems probable that the percentage of 

 sulphatids is actually higher in the cerebrum of birds of about 

 205 days than in those of about 600 days (table 5). Although 

 the series as a whole indicates that lower sulphatids signifies 

 younger age, we do not seem warranted in applying this rule to 

 brains of 200 to 600 days old. (This is in no way contradictory 

 to W. Koch's conclusion that phosphatids and sulphatids in- 

 crease in the brain of the growing animal.) 



Phosphatids and sulphatids, however, require a further remark. 

 When the amounts of phosphatids (lipoid-phosphorus) and sul- 

 phatids (lipoid-sulphur) are calculated respectively in terms of 

 percentage of total phosphorus and total sulphur (table 7), the 



9 The cerebellum-medulla of 598 and of 600 days constitute a further exception. 

 These have less lipoid-phosphorus than their corresponding (normal and ataxic) 

 groups of 205 and 206 days (table 5). Possibly in the pigeon the cerebellum- 

 medulla is chemically a more fully differentiated 'brain tissue,' and attains its 

 chemical differentiation earlier than the cerebrum. 



10 A similar situation has been found for the brain phosphatids of the rat 

 (Koch and Koch, '13). 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 31, NO. 2 



