1865.] Dr. Davy on the Temperature, fyc., of Birds. 443 



From a third fowl, a cock weighing ten pounds and three-quarters, killed 

 in the same manner as the last, the air from the humerus, measuring one- 

 tenth of a cubic inch, consisted of 15 oxygen and 85 azote. 



From the humerus of a rook, a few minutes after the bird had been shot, 

 the air obtained, measuring '22 cubic inch, was composed of 11 carbonic 

 acid, 89 azote. 



From the humerus of a tawny owl, three days after the death of the bird 

 by drowning, the air collected consisted of 5*5 carbonic acid, 5'5 oxygen, 

 89 azote. 



Though these results are not so uniform as might be expected, they seem 

 to prove that the air in the bones undergoes the same change as in the air- 

 sacs, and that there is an absorption, more or less, of the carbonic acid 

 formed by the blood contained in the vessels of the lining membrane, the 

 quantity varying according to circumstances. It may be conjectured that 

 the difference in the results may partly be owing to the air-passage, the fo- 

 ramen or foramina, in the head of the bone, being more free in some in- 

 stances than in others 



III. On Pulmonary and Cutaneous Aqueous Exhalation. 



The loss of water by exhalation from the lungs in the air expired, and 

 from the cutaneous covering of the body by evaporation, must be con- 

 sidered material elements in the problem of the animal heat of birds. And 

 inasmuch as birds drink but little, inasmuch as their skin generally is very 

 thin, dry, and little vascular; further, as the air in expiration has to 

 pass over a considerable length of surface of comparatively low tempera- 

 ture before it enters the open air, their loss of heat owing to these condi- 

 tions must be small, and more especially so, taking into account the 

 admirable covering of feathers, such bad conductors of heat, with which 

 they are provided. 



The only experiments I have to describe bearing in part on what has 

 just been stated, chiefly the last-mentioned, are the following on the rate 

 of cooling. 



Two fowls, hens of the same brood, were selected for trial. The weight 

 of each after loss of blood, having been killed by the division of the great 

 cervical vessels, was five pounds. The temperature of one (No. I), ascer- 

 tained just before, was 107' 25 in recto ; of the other (No. 2), 108. The 

 latter was rapidly deprived of its feathers, with the exception of the wings, 

 whilst on the other they were left on. Both were suspended by the legs, 



* I have occasionally found a delicate transparent membrane connecting some of the 

 eincelli. Invariably the opening into the humerus is obstructed by the muscle attached 

 to the cavity in which the foramen or foramina above mentioned are situated. Mr. Hunter 

 found when the trachea of a cock was tied, and " the wing cut through the os humeri," 

 the passage of air to the lungs was so difficult as to render it impossible for the animal 

 to live longer than to prove that it breathed through the cut bone. Observations on 

 certain parts of the Animal Economy, p. 82. 



2 L2 



