48 GASTRIC JUICE. 



cleaned, I detached from it the portion of mucous membrane in 

 which the gastric glands chiefly lie. 



As this piece of mucous membrane still contains a tolerably 

 thick layer of submucous areolar tissue, or of the so-called vascular 

 coat, in which the gastric glands are in a manner imbedded, this 

 cannot be at once employed in the preparation of the digestive 

 fluid, since then a quantity of digested gelatinous substance would 

 be mixed with it. This source of error cannot be entirely avoided, 

 since in every mode of treatment heterogeneous elements of tissue 

 will be mixed with the glandular contents. Tn order, however, to 

 obtain the latter in as pure a state as possible, the piece of mucous 

 membrane, after lying for an hour or two in distilled water at the 

 ordinary temperature, must be gently scraped with a blunt knife 

 or spatula ; the pale greyish-red, tenacious mucus which adheres 

 to the blade must be placed in distilled water, and the mixture 

 must be kept at the ordinary temperature for two or three hours, 

 being frequently shaken in the interval : a little free acid must 

 then be added, and the mixture placed for half-an-hour or an hour 

 in a hatching-oven at a temperature of from 35 to 38. By this 

 time, the fluid will be found to have lost much of its viscidity, and 

 it is now only slightly turbid ; it passes readily through the filter, 

 in the form of a perfectly limpid fluid with a scarcely perceptible 

 yellow tint. 



These and similar artificial mixtures are of much service, as 

 experience has indeed fully shown, in the investigation of different 

 conditions and phenomena in relation to digestion ; but they are 

 far less suited than gastric juice discharged from the living animal 

 for experiments having for their object to isolate as much as 

 possible from the unessential ingredients, and to render fit for 

 chemical analysis, the true digestive principle, or the group of 

 substances which constitute it. If the gastric juice from the living 

 animal be always mixed with a little saliva, that fluid interferes far 

 less with an accurate analysis than the albumen and the different 

 peptones in the artificial digestive fluids: and even if we could 

 separate the albumen, the peptones would still be associated with 

 the digestive principle, as indeed they are even with the natural 

 gastric juice, although in a far less degree. Notwithstanding the 

 labours of many observers, it appears by no means impossible 

 that by repeated investigations we may so limit the digestive 

 principle as to find a chemical expression for it, whether we can 

 exhibit the actual substance or not. Frerichs, in his classical 

 article on digestion, has hit upon the right line of investigation 



