COMPOSITION OF BEAIN OF ATAXIC PIGEONS 93 



group. Further, until exact information as to the nature of the 

 changes in the (smaller) ataxic brains are made known by neuro- 

 logical study (Hoshino), it does not seem practicable or profitable 

 for us to attempt to evaluate the influence of the brain-size dif- 

 ferences, which are present in some of the samples, upon the 

 chemical data obtained by us. 



Chemical criteria of under-differentiation or immaturity in pigeon 



brain 



In the presentation of our earlier results ('18) we endeavored 

 to make a comparison of the observed chemical differences of 

 ataxics and normals in terms of known or expected changes due 

 to age. It seems advisable to follow the same plan in the present 

 paper. At the time of our earlier publication we had only the 

 five different ages (only two of which were brains of normal birds) 

 represented in our own analyses to guide us as to the actual 

 nature and direction of chemical changes due to age in the pigeon 

 brain. The brains utilized by us ranged between the relatively 

 narrow limits of 106 days and 183 days. As a check and as a 

 more complete guide to the direction followed by chemical change 

 in brain tissue with increasing age, we utilized (and freely quoted) 

 two available series of results on other animals. Human brains 

 (Koch and Mann, '07) aged six weeks, two years, and nineteen 

 years, and rat brains (W. Koch and M. L. Koch, '13) aged one to 

 120 days — all of which were analyzed by methods essentially the 

 same as those used by us— were our only additional guides. 



Realizing the need for specific and positive knowledge of the 

 course of chemical differentiation in the pigeon brain in still 

 younger and in much older ages in our present study, we have 

 examined the brains of normal birds aged (averages) 45, 205, 598, 

 and 2,021 days. As a result of these additional analyses, we can 

 now see that several of the most pronounced chemical changes, 

 which elsewhere are known to accompany increased age in brain 

 tissues, were largely completed in the youngest of the brains 

 utilized in our former study. And further, it has now become 

 plain that some chemical fractions (extractives, sulphatids, and 



