144 DIGESTION. 



of food, already contains some albuminose in solution, it presents 

 the same reaction. If such gastric juice be mixed with a small 

 quantity of glucose, and Trommer's test applied, no peculiarity is 

 observed on first dropping in the sulphate of copper ; but on adding 

 afterward the solution of potassa, the mixture takes a rich purple hue, 

 instead of the clear blue tinge which is presented under ordinary 

 circumstances. On boiling, the color changes to claret, cherry red, 

 and finally to a light yellow; but no oxide of copper is deposited, and 

 the fluid remains clear. If the albuminose be present only in small 

 quantity, an incomplete reduction of the copper takes place, so that 

 the mixture becomes opaline and cloudy, but still without any well 

 marked deposit. This interference will take place when sugar is 

 present in very large proportion. We have found that in a mix- 

 ture of honey and gastric juice in equal volumes, no reduction of 

 copper takes place on the application of Trommer's test. It is 

 remarkable, however, that if such a mixture be previously diluted 

 with an equal quantity of water, the interference does not take 

 place, and the copper is deposited as usual. 



Usually this peculiar reaction, now that we are acquainted with 

 its existence, will not practically prevent the detection of sugar, 

 when present ; since the presence of the sugar is distinctly indi- 

 cated by the change of color, as above mentioned, from purple to 

 yellow, though the copper may not be thrown down as a precipi- 

 tate. All possibility of error, furthermore, may be avoided by 

 adopting the following precautions. The purple color, already men- 

 tioned, will, in the first place, serve to indicate the presence of the 

 albuminoid ingredient in the suspected fluid. The mixture should 

 then be evaporated to dryness, and extracted with alcohol, in order 

 to eliminate the "animal matters. After that, a watery solution of 

 the sugar contained in the alcoholic extract will react as usual with 

 Trommer's test, and reduce the oxide of copper without difficulty. 



Another remarkable property of gastric juice containing albu- 

 minose, which is not, however, peculiar to it, but common to many 

 other animal fluids, is that of interfering with the mutual reaction 

 of starch and iodine. If 3j of such gastric juice be mixed with 3j 

 of iodine water, and boiled starch be subsequently added, no blue 

 color is produced ; though if a larger quantity of iodine water be 

 added, or if the tincture be used instead of the aqueous solution, 

 the superabundant iodine then combines with the starch, and pro- 

 duces the ordinary blue color. This property, like that described 

 above, is not possessed by pure, colorless, gastric juice, taken from 



