104 MATHILDE L. KOCH AND OSCAR RIDDLE 



Our data concerning the localization of the derangement in the 

 brain are still imperfect, because in our analyses the brain was 

 separated into anterior and posterior parts only. It has been 

 made clear that the chief size reductions occur in the posterior 

 brain; and the evidence indicates that the deviations in chemical 

 composition are accentuated in this same region. 



Whether analyses of medulla and cerebellum separated from 

 each other would have shown that all of the size and chemical 

 changes occurred in one only of these organs is a question quite 

 unanswered by our data. Nevertheless, the fact that changes 

 were also found in the cerebrum would seem to indicate that the 

 derangement is not absolutely confined to either of the chief 

 divisions of the brain. It is possible, however, that localized 

 affected areas are present and that these were 'diluted' by much 

 normal material in our samples as prepared for analysis. If this 

 were true, these particular localized areas would necessarily have 

 a much greater degree of chemical under-differentiation than is 

 indicated by the figures obtained by us. 



The sex of the ataxic birds deserves a further statement. 

 Those who may have carefully examined the character of the 

 samples obtained from ataxic pigeons, in both the earlier and pres- 

 ent series, will have noted that more female brains than male 

 brains are found in these samples as prepared for analysis. In 

 the earlier series (of ataxics) the proportion was ten females to 

 five males; in the present series twelve females to eight males. 

 This disproportionate representation of the two sexes in these 

 samples was not consciously effected by us, since the sex of most 

 of the individuals selected for the purpose was not known until 

 after the birds were killed. In most cases they were selected 

 chiefly because they were ataxic in one or another degree. Equal- 

 ity of the sexes was desired in our present samples, but could not 

 always be obtained. 



The excess of females in the two series of ataxics has led us to 

 examine a segment of the breeding data in an effort to learn 

 whether the ataxia more often occurs in females than in males. 

 The data given below were obtained from a tabulation 15 of the 



15 All groups of offspring of ataxic blood or strain were included in the sum- 

 mary. The rnatings which had yielded no ataxic offspring were excluded. 



