108 MATH 1 1,1)10 L. KOCH AND OSCAR RIDDLE 



The 'age series 1 of pigeon brains 



It has earlier been stated that it is only on the brains of man 

 and the rat that we have had fairly adequate data for the pro- 

 gressive change of the various proximate chemical constituents 

 during growth, or, more properly, as related to growth and age. 

 The present work supplies such an 'age series' for the pigeon 

 brain, and I his series is now as extensive as are those now known 

 for man and the rat. Each of these latter series includes obser- 

 vations on one or more relatively younger stages than we have 

 studied in the pigeon. On the other hand, the data for the pigeon 

 include one relatively older stage than has been obtained on 

 either of the other two forms. 



Except for differences which appear because of a lack of paral- 

 lelism of age, the three 'age series' show that quite the same course 

 of chemical differentiation is followed in the brain of man, the 

 rat, and the pigeon. It is not our purpose to discuss these three 

 series here. The essential similarity of results obtained on mate- 

 rial from sources so unlike should, however, be noted as additional 

 evidence for the trustworthiness of the methods developed by W. 

 Koch ('()<)) for brain analysis. The brains of the three 'age 

 series' mentioned above have all been analyzed according to 

 Koch's method. 



Since the above was written, we have had an opportunity to 

 learn something of the results of the neurological studies made 

 by Hoshino ('1!)) of the brains of some of this same family of 

 ataxic pigeons. Although the present study was completed and 

 fully described before we were aware of Hoshino's results, 17 it 

 seems well to add here that the neurological and chemical studies 

 support an essentially similar view. The bearing of Hoshino's 

 summary statement is self-explanatory: "This may be regarded 

 as a hypoplasia or developmental inhibition in the propriocep- 

 tive system, pari of the motor system, and some structures con- 

 necting (lie medulla oblongata and cerebellum, occurring during 

 growth, with scarcely any definite degeneration or secondary 

 increase of neuroglia tissue." 



17 The courtesy of Doctor Hoshino has made it possible for US to read his com- 

 pleted manu crip! prior to its publication. 



