EFFECT OF THYROID FEEDING. 283 



the development of the feather, differentiation but not cornifica- 

 tion had been omitted. 



Riddle (1907) distinguished five types of defect in feather 

 structure, two being represented by Strong's cases, a third by a 

 very inconspicuous transverse depression or line without defects 

 in barbules, a fourth by constrictions in the feather germ, and a 

 fifth by a single instance of a feather with barbs broken off at 

 even distances from the shaft, the defect extending parallel to 

 the rhachis. 



The first three of these are of widespread occurrence among 

 birds. Riddle discussed them in connection with what Whitman 

 had called fundamental bars (alternating lighter and darker 

 transverse bands of pigment) so beautifully figured in his posthu- 

 mous paper (1919, pis. 72-75). He concluded (1908) on the 

 basis of experiments, that both are referable to variations in the 

 nutrition of the feather germ during its development, the funda- 

 mental bars being produced by diurnal changes in blood supply, 

 the fault bars by defective nutrition through this and other 

 agencies. In his experiments, reducing the food, feeding Sudan 

 III, mechanical destruction of tissues and blood vessels and the 

 administration of amyl nitrite were all effective. 



We have no satisfactory evidence of variation in the blood 

 pressure of our birds. But we have seen abnormalities in feather 

 structure belonging to Riddle's fifth type as a direct consequence 

 of starving two White Leghorn males. One of our adult male 

 Brown Leghorns on a daily ration of i gm. of dessicated thyroid 

 replaced three pairs of remiges with feathers of normal length 

 but abnormal in structure and color. The vanes were narrower 

 and proximally misshapen as though fashioned under cramped 

 conditions. The normal color was almost entirely lacking, the 

 feathers being prevailingly white. There appears to be no reason 

 to doubt that directly or indirectly such defects are referable to 

 disturbed nutrition. We have also two rectrices from an adult 

 Rhode Island Red female nearly two years old that resembles 

 Strong's feather with a "tassel-like appendage." One of these 

 rectrices is marked with great regularity by transverse depres- 

 sions belonging to Riddle's third type of feather defect. At the 

 distal end of the "appendage" two or three of these are definitive 



