DIGESTION 187 



the stomach of the horse is remarkable ; it adheres to the villous 

 coat like unboiled white of egg, and cannot be washed away, 

 even by a powerful jet of water. The amount secreted is un- 

 known, but must be considerable ; less is formed during hunger 

 than during activity, and there is less in ruminants than in 

 horses. 



Gastric Juice. — It is only lately that a pure sample of gastric 

 juice (but not from the horse) has been available for analysis. 

 Most of the previous secretions examined have been a mixture 

 of saliva, gastric juice, and perhaps other substances. Pawlow 

 devised a method by which the stomach of the dog could be 

 rendered available for physiological inquiry, and a pure secretion 

 was obtained (see Figs. 68 and 69). 



Py lorus s <S\[\(/ I /Oesophagus 



Fig. 68. — Pawlow's Stomach Pouch. 



A, B, Line of incision ; C, flap for forming the stomach pouch. At the base of 

 the flap the serous and muscular coats are preserved, and only the mucous 

 membrane divided, so that the branches of the vagus going to the pouch are 

 not severed. 



Pure gastric juice in the dog is as colourless as water, and 

 possesses a specific gravity of 1002 to 1004 ; it is thin — that is 

 to say, is not mucinous — and of a strongly acid reaction. 

 Chemically it consists of acid and enzymes ; it contains 0-4277 per 

 cent, of dried material, of which 0-1325 is ash. The latter con- 

 tains 24 per cent, potassium, 19 per cent, sodium, and 0*18 per 

 cent, calcium. The acid, which is hydrochloric, amounts to 

 0-46 to 0-56 per cent., gastric juice being the only secretion in 

 the body containing a free acid. Pawlow states that the total 

 chlorine contents of the secretion are twice that found in blood, 

 and that he has obtained 5 grammes chlorine from the secretion 

 in 3 J hours — an amount equal to that in the entire blood. There 



