126 THE BODY AT WORK 



ill-chewed cucumber or apple. The pyloric valve of the stomach 

 is forbidden to allow any lumps of food to pass until the very 

 last stage of gastric digestion. Pieces of ill-masticated vege- 

 table tissue lie for a long time in the stomach, irritating the ends 

 of the gastric nerves, until at last the time comes for them to 

 be shot through the pylorus into the duodenum. Many salts 

 which vegetables contain, especially the earthy carbonates 

 and phosphates, are dissolved by the acid of the gastric juice. 

 JVEeat consists of muscle-fibres supported by connective 

 tissue. In the stomach the gelatiniferous connective tissue 

 is dissolved, setting the fibres free. Further, the fibres being 

 surrounded by a membrane of the same nature sarcolemma 

 this is removed ; and although it may be hardly justifiable to 

 speak of " Krause's membranes " (cf. Fig. 10) as gelatiniferous 

 septa, the fibres are certainly composed of segments Bow- 

 man's discs, sarcous elements into which they break up under 

 the action of gastric juice. As a result, meat-fibre is reduced 

 to a finely divided granular condition. The capacity of gastric 

 juice for dissolving collagen (the substance of which connective 

 tissue is composed) may be regarded as its most characteristic, 

 as it is one of its most valuable, properties. Collagen, when 

 boiled or acted on -by acids, takes water into its molecule, 

 becoming gelatin. Under the influence of gastric juice gelatin 

 is rapidly hydrolysed into diffusible gelatin-peptone. Pan- 

 creatic juice is unable to act upon collagen, unless it has been 

 previously boiled, or swollen by the action of dilute acids. 



Fat is composed of vesicles of oil supported by connective 

 tissue. Gastric juice, by dissolving the connective tissue and 

 the collagenous walls of the vesicles, sets the oil free. The oil, 

 even though it be as firm as suet when cold, is liquid, or almost 

 liquid, at the temperature of the body. 



Thus, with the exception of raw vegetables, the hard fibre 

 of cooked vegetables, elastic tissue of meat, and a few other 

 indigestible substances, the meal is reduced in the stomach to 

 a cream-coloured, fatty, strongly acid " chyme." In this 

 condition it enters the duodenum, where it at once comes 

 into contact with an alkaline secretion. The passage of acid 

 chyme down this portion of the canal provokes the discharge 

 of gushes of bile and pancreatic juice. By precipitating 

 partially digested proteins and " acid-albumin " bile renders 



