GENESIS OF FAULT-BARS IN FEATHERS. 3 5 I 



a relative high pressure during the day and a low pressure at 

 night. I give these a priori reasons for believing that a low 

 blood pressure exists in birds at night because some may not be 

 disposed to accept this as proved on my evidence alone. 



To me it seems that the result of the amyl nitrite experiment 

 proves much more than that a lowering of the blood pressure 

 will produce fault- bars. It is significant that the fault-bars pro- 

 duced by the amyl nitrite were superposed upon the defective lines 

 (and not on the fundamental bar between them) belonging to the 

 particular days of the experiment (as was determined by subse- 

 quent examination). From this we can say with absolute cer- 

 tainty that the faidt-bars are normally laid down at night. Further- 

 more, the smaller, "normal" low pressures must be accredited 

 with the same action as these observed extremely low pressures 

 and are, therefore, to be associated with the less obvious defective 

 lines which are produced daily ; they exert their action in the 

 same direction, but to a smaller extent. 



In this connection we may quote Tigerstedt's l statement con- 

 cerning the blood pressures of poorly nourished animals. This 

 author states that " schlecht ernahrte Thiere haben einen niedri- 

 gern Blutdruck als kraftige Individuen derselben Art." 



Finally, we may state the following inter-related facts, which 

 go very far toward proving that a low blood pressure normally 

 occurs at night in birds: 2 (i) Diminished feeding of birds pro- 

 duces emphasized fault-bars. (2) Artificially reduced (amyl 

 nitrite) blood pressures produce equivalent defects. (3) The 

 fault-bars are universal in feathers. (4) The fault-bars are pro- 

 duced at night. (5) The lowest daily temperature in birds occurs 

 from 1:00 A. M. to 5:00 A. M. (6) Other physiological condi- 

 tions of the bird seem to be favorable at night for the production 

 of low blood pressures. (7) A lowering of the pressure would 

 reduce the food-supply and have a tendency to produce defects. 



Material for a direct demonstration of the daily blood pressure 

 curve has unfortunately not been available. That its minimum 



1 Tigerstedt, R., " Lehrbuch der Physiologie des Kreislaufs," Leipsic, 1893. 



2 Simpson and Galbraith whose work is cited below find that the temperature curve 

 of the owl (nocturnal) is reversed. If this is true the blood pressure curve of this bird 

 may also be reversed, and the fault-bars (and light fundamental bars) produced prob- 

 ably in the afternoon. 



