Proceedings of Learned Societies. 129 



ed every thing they could feed on, these Field-fares roust have 

 returned here for a short time, iu consequence of the inclemency 

 of the weather ahroad. Red-wings and Field-fares always leave 

 this country when they are in the best condition. The approach 

 of severe frost is indicated by the arrival of water-birds, as that of 

 thaw is by the coming of the spring migrators. Birds often out- 

 strip in their migrations the progress of the frost itself. Dr. Jen- 

 ner considered that Dr. Darwin must have been mistaken in what 

 he says respecting Cuckoos seen feeding their young. The birds 

 in question must have been Goat-suckers, which are very easily 

 confounded with Cuckoos by those who are not fully conversant 

 with the characters of their plumage, &c. 



This very interesting paper concluded with a recapitulation of 

 the principal facts contained in it, and of the author's views re- 

 specting them. 



Dec. 11. — A paper was communicated, On the Nature of the 

 Acid and Saline Matters usually existing in the Stomachs of Ani- 

 mals; by William Prout, M.D. F.R.S. 



The object of this paper was to prove, that the acid usually 

 found to exist in the stomach of animals during the digestive pro- 

 cess is the muriatic acid, and that the saline matters consist chiefly 

 of the alkaline muriates. 



The method adopted by the author to prove this, was to digest 

 the contents of the stomach of a rabbit, or other animal, in distilled 

 water as long as they imparted any thing to that fluid. The solu- 

 tion was then divided into four equal portions. The first of these 

 was evaporated to dryness in its natural state, and the residuum 

 burnt, by which means the muriatic acid in union with a. fixed 

 alkali was ascertained. Another portion was super-saturated with 

 potash, evaporated to dryness, and burnt as before, and thus the 

 total quantity of muriatic acid present determined. A third por- 

 tion was exactly neutralized with a solution of potash of known 

 strength, which gave the proportion of free acid present. A fourth 

 portion was reserved for miscellaneous experiments. From the 

 results thus obtained, checked by others, the author was enabled 

 to ascertain the proportion of muriatic acid present, whether in 

 union with a fixed or volatile alkali, or in an unsaturated state f 

 Vol. I. i 



