Dr. Mitchell on the Occurrence of Sugar in the Animal Economy. 85 



20th February, 1850. — Tlie President in the Chair. 



The following were elected members : — Messrs. William Brand, James 

 George Morison, William Rae Arthur, John Burns Bryson, David Cross. 



Professor William Thomson gave an experimental demonstration of 

 Mr. James Thomson's theoretical conclusion, that the freezing point of 

 water is lowered by pressure. 



The following paper was read : — 



XII. — On the Occurrence of Sugar in the Animal Economy. By 

 Arthur Mitchell, A.M., M.D, 



The importance of any new fact bearing on the subject of digestion, 

 will, I trust, be received as my apology for reading to the Society the 

 following paper. The subject belongs more peculiarly to the physiologi- 

 cal section, but as the aid of chemistry has been constantly called in 

 during the progress of the investigations, and as the works of Liebig have 

 now rendered these subjects more or less commonly understood, I hope it 

 may not be altogether uninteresting to the members generally. 



To Liebig, Payen, and to the learned professor of Strasbourg, M. 

 Persoz, as well as to Lassaigne, Bouchardat, Mialhe, and more recently 

 to Bernard and Barreswill, we are indebted for the knowledge of facts 

 with regard to the transformations which the saccharine aliments undergo 

 in the process of digestion, of the highest physiological interest. 



Amongst these is one now universally admitted ; I refer to the cata- 

 lytic power, which the salivary and pancreatic fluids possess of converting 

 starch into sugar. Since their researches, however, it has been shown by 

 Magendie that the same property belonged to almost all the fluids of the 

 economy, such as the bile, urine, gastric juice, serum of blood, spermatic 

 fluid, &c. Moreover, on making infusions of portions of brain, heart, 

 lung, liver, kidney, muscle, &c., and adding these to solutions of starch, 

 the transformation was found to be equally complete. 



Having observed that the serum of blood acted thus on feculents, after 

 it had been drawn from the body, the same observer was naturally led to 

 inquire if, while circulating in the animal, it could efi"ect the same change. 

 Accordingly, a quantity of starch was injected into the jugular vein of a 

 rabbit, and in less than ten minutes afterwards a portion of blood was 

 withdrawn for examination. Not the slightest trace of starch, however, 

 could be detected; but, apparently in its place, there existed a large 

 amount of sugar. (That the origin of this sugar might not seem to be 

 the food which the animal had last eaten, Magemdio had the precaution 

 to take, as the subject of this experiment, a rabbit which had been fasting 

 for three days.) 



After the flrst bleeding, successive quantities were abstracted at 

 intervals of an hour, and subjected to analysis ; and it was found that for 



