

Royal Society. 459 



chamois-leather, and dissolving the mercury in dilute nitric acid 

 with gentle heat. The compound is left in the form of four- 

 sided prisms of the most brilliant metallic lustre, which may be 

 boiled in nitric acid without decomposition, and exposed to the 

 atmosphere for months without becoming tarnished. On ex- 

 posure to heat they do not fuse, but afford a sublimate of metallic 

 mercury, amounting in my experiments to rather less than 12 per 

 cent. ; the form of the crystals remained unaltered, their lustre 

 was little affected, and the residue consisted of pure gold. This 

 would correspond to a compound of four atoms of gold to one of 

 mercury : — 



Au . . . 197x4=788 or 88-74 

 Hg . . . 100 100 ... 11-26 



888 10000 



LXVI. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 398.] 

 Feb. 1, 1855.— Colonel Sabine, Treas. and V.P., in the Chair. 



THE following communication was read : — 

 " Micro-chemical Researches on the Digestion of Starch and 

 Amylaceous Foods." By Philip Burnard Ayres, M.D. Lond. 



After some general historical remarks on the methods hitherto 

 employed in the investigation of the complicated phenomena of the 

 process of digestion, the comparatively small results obtained by 

 chemical analysis of the contents of the stomach, intestinal canal, and 

 of the evacuations, by Tiedemann and Gmelin, Berzelius, and others, 

 the author proceeded to demonstrate the necessity of a minute ex- 

 amination of the contents of the alimentary canal by the microscope, 

 and such chemical tests as we possess for the determination of the 

 changes of such articles of food as exhibit definite structure. 



In order that we may ultimately arrive at a complete exposition 

 of the phenomena of digestion, he is of opinion that it will be neces- 

 sary to examine, — first, the structure of particular kinds of food, 

 then the changes produced in them by cooking, and lastly to trace 

 the changes they undergo at short intervals, through the alimentary 

 canal from the stomach to the rectum. The results of a series of 

 researches of this character on the changes in starch, and starch- 

 containing foods, are presented in this memoir. 



The method adopted for the examination of the changes in starch 

 and starch-foods was as follows : — An animal was kept fasting 

 twenty-four hours, and afterwards confined to a diet consisting of 

 the starcli or amylaceous food, with water, for five or six days, until 

 the cicbris of all other kinds of food previously taken were cleared 

 from the alimentary canal. At a determinate time, after a meal, 

 the animal was killed, the abdomen laid open as quickly as possible, 



