46 Dv Davy on the 



of British Guiana, so productive without manure, in part 

 owes its fertilit}^, as well as in pai't to the extreme minute- 

 ness of division of the inorganic earthy portion, its principal 

 constituent. Believe me, my dear Sir, very faithfully yours, 



J. Davy. 



Barbadoes, August 15, 18i7. 



On the Urinary {Secretion of certain Animals, considered in 

 connection with their Temperature, Food, ^'c. By JOHN 

 Davy, M.D., F.R.S. Lond. & Ed., &c. 



1. It is well known that the urinary secretion in the in- 

 stance of many birds, — animals exceeding all others in tem- 

 perature, — consists chiefly of lithate of ammonia. So far as 

 my inquiries have extended, I have not met with a single ex- 

 ception ; even in the case of birds, as the parrot and the dove, 

 living in confinement, restricted to a diet entirely vegetable, 

 I have found it the same. The dove, in the particular in- 

 stance to which I allude, was fed on Guinea and Indian corn, 

 the parrot on bread and fruit, chiefly the plantain ; and other 

 parrots of several kinds, the urine of which I examined in 

 Ceylon many years ago, and was found similar, were fed 

 chiefly on rice and plantains. 



2. Insects, with a variable temperature, varying, it would 

 appear, with the degree of their excitement, or energy of ac- 

 tion, or of respiration, whether living on vegetable or animal 

 matter, or on a mixture of the two, have, according to my ex- 

 perience, a urinary secretion like that of birds, composed 

 chiefly of lithate of ammonia and lithic acid. 



3. Spiders, of low temperature, but of considerable activity, 

 living entirely on insects, secrete a urine of a difi'erent kind, 

 being composed, as I have found it, of xanthic oxide. 



4. Serpents, of low temperature, a few degrees only above 

 that of the atmosphere in which they live, occasionally, like 

 the spiders, making great muscular exertions, and, like them, 

 capable of living a long time without food, andtheir food be- 

 ing entirely animal, have their urinary secretion composed 

 chiefly of lithate of ammonia. 



