442 Dr. Davy on the Temperature, $c., of Birds. [1865. 



is a certain loss of carbonic acid, a loss equivalent to the proportion of 

 oxygen less than exists in the atmospheric air inspired ; and it may be in- 

 ferred that the deficient carbonic acid was absorbed and retained in the blood; 

 and that it was so, was indicated by the very dark colour of the blood ob- 

 tained by the division of the great cervical vessels immediately after the 

 extinction of life, and further by the large quantity of air that was disen- 

 gaged from the blood when subjected to the air-pump *. 



2. Of the air from the air-sacs. On the air from these receptacles I 

 have made the following experiments : 



From a turkey killed by drowning, a portion of air was collected by a 

 puncture made under water into the air-vesicles under the sternum. It was 

 found to consist of 15*5 carbonic acid, 84*5 azote. 



From a duck deprived of life in the same manner, a portion of air was 

 obtained from the abdominal air-receptacles. It was composed of 10*52 

 carbonic acid, 5' 26 oxygen, 88'32 azote. 



These results would seem to warrant the inference that the very delicate 

 membrane of which the air-receptacles are formed, is like that of the air- 

 cells of the lungs pervious to air ; and the further inference, that the defi- 

 cient carbonic acid in the air examined was owing to its absorption by the 

 blood. 



3. Of the air contained in the bones. The experiments I have made on 

 this air have been confined chiefly to that of the humerus. I may premise 

 that in every instance in which I have examined the lining membrane of 

 the hollow bones of birds (the air-containing bones), I have found it dis- 

 tinctly vascular ; in this respect differing from the membrane of the ail* 

 receptacles communicating with the lungs situated in its thoracic and ab- 

 dominal cavities. Not unfrequently, both in the humeri and femora, the 

 vessels have had the appearance of being varicose, and this when the ex- 

 amination was made a few minutes after death. 



From the humerus of a common fowl, killed by drowning, a portion of 

 air obtained was found to be composed of 4' 7 oxygen, 95'3 azote. The 

 bone was dissected out under water, and its head there removed to allow 

 free exit to the included air. 



From the humerus of another fowl killed by the division of the great 

 cervical vessels, the air procured consisted of 8'3 carbonic acid, 8'3 oxygen, 

 83 '4 azote. In this instance the bone was dissected out underwater, whilst 

 the fowl was still warm. No air escaped until the delicate bony tissue (the 

 reticulated structure) was broken through, and indeed then but little, 

 until the head of the bone had been removed. 



* Two trials of the blood were made, one in which the blood was received in water 

 previously purged of air, the other in which it was received in weak solution of potassa, 

 also exhausted of air by the pump : the difference was remarkable, so much air being 

 disengaged from the first, so little from the second. 



It may be deserving of mention that in the instance in which the blood diluted with 

 water was allowed to coagulate, no air was disengaged by the action of the pump until 

 the resisting clot was broken up, when the disengagement on exhaustion was copious. 



