482 THE GASTRIC JUICE. [CH. xxxi. 



gastric juice : this is derived by fermentative processes from the 

 food. 



Hydrochloric acid is absent in some diseases of the stomach ; the best 

 colour tests for it are the following : 



(a) Gunsberg's reagent consists of 2 parts of phloroglucinol, I part of 

 vanillin, and 30 parts of rectified spirit. A drop of filtered gastric juice is 

 evaporated with an equal quantity of the reagent. Red crystals form, or if 

 much peptone is present, there will be a red paste. The reaction takes 

 place with i part of hydrochloric acid in 10.000. The organic acids do not 

 give the reaction. 



(Z>) Tropaeolin test. Drops of a saturated solution of tropaeolin -oo in 

 94 per cent, methylated spirit are allowed to dry on a porcelain slab at 40 C. 

 A drop of the fluid to be tested is placed on the tropaeolin drop, still at 

 40 C. ; and if hydrochloric acid is present, a violet spot is left when the 

 fluid has evaporated. A drop of o - oo6 per cent, hydrochloric acid leaves a 

 distinct mark. 



. Lactic acid is soluble in ether, and is generally detected by making an 

 ethereal extract of the stomach contents, and evaporating the ether. If lactic 

 acid is present in the residue it may be identified by the following way : 



A solution of dilute ferric chloride and carbolic acid is made as follows : 



10 c.c. of a 4-per-cent. solution of carbolic acid. 



20 c.c. of distilled water. 



I drop of the liquor ferri perchloridi of the British Pharmacopoeia. 



On mixing a solution containing a mere trace (up to I part in 10.000) of 

 lactic acid with this violet solution, it is instantly turned yellow. Larger 

 percentages of other acids (for instance, more than o - 2 per cent, of hydro- 

 chloric acid) are necessary to decolorise the test solution. 



The Innervation of the Gastric Glands. 



As long ago as 1852 Bidder and Schmidt showed in a dog 

 with a gastric fistula that the sight of food caused a secretion of 

 gastric juice; and in 1878 Richet observed' that in a man with 

 complete occlusion of the gullet, the act of mastication caused a 

 copious flow of gastric juice. There can therefore have been no 

 doubt that the glands are under the control of the nervous 

 system, but until quite recently all attempts to discover the 

 secretory nerves of the stomach proved unsuccessful. Pawlow 

 solved the problem by experiments on dogs : he first made a 

 gastric fistula ; and a few days later exposed the oesophagus, 

 divided it, and sewed the two cut ends to the two corners of the 

 wound in the neck. The animal was fed by means of the lower 

 piece of the ossophagus ; but any food taken by the mouth or 

 any saliva secreted into the mouth was never allowed to enter the 

 stomach, but fell out of the opening of the oesophagus in the 

 neck. These animals were kept alive for months and soon 

 accommodated themselves to their new conditions of life. 



If one of them was kept without food for a few hours, and 

 then given a meal of meat, it devoured it with avidity though 

 none ever reached the stomach. The effect of this sham feeding 



