A STUDY OF FUNDAMENTAL BARS IN FEATHERS. 1/3 



attempt to explain the causes for the nightly fall of the blood- 

 pressure in birds. Let it suffice to say that we find a parallel 

 phenomenon in mammals. I wish further to call attention to the 

 fact that my demonstration that the lowest blood-pressure in 

 birds falls at night is evidence that the blood-pressure and tem- 

 perature curves of birds are similar curves, as they are known 

 to be in mammals. Of course, I have not showed a blood- 

 pressure curve for birds ; I have, however, located in a general 

 way the time of its minimum. I am in a position to confirm the 

 observations of Conn and Van Beneden l as to the temperature 

 cu-rves of birds. They worked 

 with pigeons. I have tempera- 

 ture curves essentially similar to 

 theirs, from ducks, ring-doves, P"\ 

 and from chicks both old and z&J 

 young. The lowest temperature 

 occurs at about four to five o'clock 



Loiv Blood-Pressure and the Nu- 

 trition of the Feather Elements. FIG. 3. Cross-section of a feather- 

 There remains to be indicated i erm in the re ion of growth. (Semi- 



, , . . , . diagrammatic, magnified about loo dia- 



some oi the histological relations , , , ,, 



meters.) f>, barb-forming cells; ble, 



of the capillaries and the feather- barbule-fonning cells; /.pigment cell; 

 elements which suffer from the ea t> capillaries; //, P ul p; /, outer 



i r , i i sheath ; i.s/i. inner sheath. 



lowering of the vascular tension. 



I shall also outline the way in which the low pressure probably 



acts. 



Just as among the vertebrates we know that certain tissues, 

 e. g-., the liver cells, are kept always on the verge of asphyxia- 

 tion, so I believe are the epidermal cells of the growing feather- 

 germ taxed to their utmost to secure from the blood enough 

 nourishment to allow the rapid cell-division to proceed in full 

 swing. Where else in an adult vertebrate do we find a more 

 rapid growth and differentiation of tissue than we find in the 

 moulting of certain birds ? We may then expect to find here a 

 struggle for food when this becomes reduced in amount, and 

 those parts nearer the blood-supply should fare better than parts 



1 Corin, G. , and Van Beneden, A., "La Regulation de la temperarure chez les 

 Pigeons," Archives de Biologie, Vol. VII., pp. 265-276, 1887. 



