ii EXTERNAL DIGESTIVE SECRETIONS 115 



(Fig. 38, B), which is united to the main stomach by the two outer wall>. 

 The two cavities lined with mucous membrane are completely separated by 

 a double septum consisting of the sutured mucous coat of the stomach and 

 that of the cup-shaped nap. The opening of the pouch is stitched to the 

 abdominal wall (A, A). 



XIII. The chemical composition of the gastric juice must be 

 studied before discussing the process by which it is formed. 



The gastric juice obtained by C. Schmidt from a healthy 

 woman with a gastric fistula, after the ingestion of peas and a 

 little water, was found to be a clear thin fluid, much less acid 

 than that of the dog, with specific gravity of 1-0022-1-0024. It 

 became slightly cloudy on boiling, and left a solid residue of 

 about 2 per cent. 



The gastric juice obtained by Fawlow and his co-workers and 

 pupils from the dog by the above method of sham feeding is 

 certainly purer, as well as that obtained from the fundus sac by 

 Tawlow's method, which preserves the integrity of the vagus 

 fibres. 



This pure secretion, which is free of all alimentary residues, is 

 as clear as water, acid, with no extraneous taste, specific gravity 

 r0030-l'0059. It turns the plane of polarisation to the left 

 (from 0'70 to 0'73 in a layer of 20 cm.). On evaporation it leaves 

 a solid residue of 0'29-0'60 per cent; 0-10-017 per cent ash on 

 combustion. It constantly contains a little protein, but no 

 peptone, leucine, nor tyrosine. On lowering the temperature it 

 becomes cloudy, and forms three layers : the top one clear, the 

 middle turbid, the lower consisting of a deposit of homogeneous, 

 highly-refracting granules. 



According to the chemical analysis made by Mme. Schumowa- 

 Siinanowskaia of the secretion obtained from the dog by sham 

 feeding, its composition is as follows : 



Acid . . 0-46-0-56 per cent. 



Chlorine 0-49-0'62 



Dry residues 0-43-0-60 



Ash ... . 0-09-0-16 



Substances coagulated by alcohol . 0'14-0'19 



Substances coagulated by boiling . 0-13-0-18 



Substances precipitated at C. . OOll-O'OOS 



Phosphoric acid ..... 0'004 



As we shall see elsewhere, the digestive activity of the gastric 

 juice is due to the hydrochloric acid and the enzymes which it 

 contains, these being the specific secretory products of the gland 

 cells. The quantitative variations of these products, and the 

 process and seat of their formation are as follows : 



(a] The acidity of the gastric juice, owing to the constant 

 presence of a free acid, is well established for all vertebrates. 

 Prout (1824) was the first who suggested that this free acid was 



