338 Dr. Davy on the Temperature 6fc. of Birds. [June 15, 



tacles and in the air contained in the bones, attributable to the same 

 cause. 



Of the third part, the subject is pulmonary and cutaneous aqueous exhala- 

 tion. From the facts brought forward, and the experiments described, there 

 appears to be proof afforded that birds perspire little and cool slowly, and 

 consequently that their high temperature is partly owing to these two cir- 

 cumstances the one (the latter) attributable to their clothing of feathers, 

 the other (the former) to the little vascularity of their cutis. 



The subject of the fourth part is the kidneys and their excretion. As these 

 organs are proportionally large in birds, and as their excretion is very much 

 less liquid than that of the mammalia, it is presumed that, from its carrying 

 off less heat, it may be considered an element in the problem of the high 

 temperature of birds, and that as the compound excreted is chiefly urate of 

 ammonia, it may conduce to a less expenditure of oxygen than if urea were 

 a constituent of their urine. 



In conclusion the author suggests that the high temperature for which 

 most birds are remarkable (not all, there being certain exceptions) may be 

 due to a combination of circumstances, some positive, some negative, the 

 positive chiefly the conversion of oxygen into carbonic acid, the negative 

 those conditions influential mainly by economizing the heat produced or 

 checking its escape. Further, it is conjectured that there may be other 

 ancillary conditions, such as a powerful heart ensuring a rapid circulation, the 

 peculiar structure of the blood-corpuscles, and the little viscidity of the 

 blood of birds. 



Some remarks are added on the pneumatic system of birds, so distinctive 

 of their class, with conjectures on its uses, these in part obscure and seem- 

 ing to require further research for their elucidation. 



The supplementary additions are given chiefly in a tabulated form, of 

 which there are five : 



The first contains a list of birds examined, altogether 64, of which 

 number 22 were found to have air in some of their bones, and 42 to be 

 without air in them. 



In the second the weight of a certain number of species is given (39), 

 and the weight of their feathers, and in most instances of their bones. 



In the third the weight of the principal bones of a selected number of 

 species (27) is stated. 



In the fourth the composition of some of the bones, as determined by 

 calcination . 



And in the fifth the weight of the principal organs of five species. 



With the exception of the last, some brief remarks are appended to each 

 Table. 



