GENESIS OF FAULT-BARS IN FEATHERS. 



353 



den, the normal condition of the birds was disturbed, and not 

 being able to rest sufficiently at night they rested later — from 

 8:00 to 12:00 — and therefore showed a falling' temperature 

 during these hours. 



The combined temperature curve for 16 birds, i. e., 6 ducks, 

 5 ring doves and 5 chicks, is here reproduced (Fig. 5). The birds 

 were under continuous observation for 48 hours. The curve ex- 

 pressses the temperature during the last 24 hours. The readings 

 taken during the first 12 hours were found to be too high and un- 

 reliable ; these were thrown out and the error of Corin and van 

 Beneden avoided. This information was gathered with a view 

 to obtaining additional data concerning the probable time of the 

 lowest blood pressure in the bird. If the diurnal temperature 



P.TD ATT] Tloon P.m. 



Fig. 5. Combined diurnal temperature curves of 16 birds. 



and blood-pressure curves in birds are similar curves — as they 

 are known to be in mammals — the temperature curve shown here 

 indicates that the lowest blood pressure in birds occurs from I :oo 

 to 5:00 A. M. If the fall in the blood pressure is as sharp and 

 of such short duration (3 to 6 hours) as is the very low temper- 

 ature, it is easy to understand how it is that only a faint, narrow 

 line is usually left to record its action. 



Since the daily variation in temperature in birds is shown to be 

 considerable — the above figures showing a lower temperature of 

 about 0.7 C. for four hours of the day than for another twelve 

 hours, — and since the fault-bars are produced during this low tem- 

 perature, it may be asked whether the reduced temperature is caus- 



