112 PHYSIOLOGY 



CHAP. 



digestive power is decidedly weaker. This digestive power de- 

 creases from the first to second, or first to seventh hours, then 

 rises again and reaches its maximum at the fifth, or according to 

 other experiments, the, eighth hour. 



Pawlow and his co-workers have recently succeeded in isolating 

 a closed pouch or cul de sac from the stomach, without injuring 

 the vagus fibres that control secretion (infra, page 114). From 

 the animals thus operated on, they have collected important data 

 relative to the influence upon the secretion of the blind sac 

 of certain alimentary substances introduced into the stomach. In 

 order to exclude reflexes by the secretory fibres of the vagus 

 excited from the surface of the mouth, pharynx, and oesophagus, 

 the food is introduced into the stomach by the sound. The results 

 may be summarised as follows : 



(a) Water, 0'1-0'5 per cent solutions of hydrochloric acid, 

 O'01-l per cent salt solutions, introduced into the stomach in 

 amounts of 100-150 c.c., produce only a very weak secretion of 

 juice in the blind sac. 



(6) Water, 0'5 per cent salt solution, 10 per cent solutions of 

 cane-sugar or starch, in quantities of 500 c.c., produce a stronger 

 secretion, which commences 13 to 29 minutes later, and lasts some 

 60 to 135 minutes. 



(c) These substances do not affect the secretion of the blind 

 sac in themselves, but in virtue of the water in which they are 

 dissolved. In fact, if plain distilled water is injected into the 

 stomach, a secretion of equal quantity and duration is evoked. 



(d) When, on the contrary, peptone is introduced into the 

 stomach by the sound (this being, as we shall see, the principal 

 product of the digestion of proteins by the gastric juice), there is, 

 after about 13 minutes on an average, an abundant secretion in 

 the pouch which lasts for some 3 hours. 



(e) Neither ov-albumin nor proteoses produce a similar effect. 

 They only cause a weak secretion for a short time, which may be 

 due to the amount of water in which they are dissolved. We may 

 conclude that peptone is a specific stimulus for the secretory 

 elements of the stomach, probably because it is capable of exciting 

 the centripetal nerve-endings of the mucous membrane, which 

 determine the secretion reflexly by the centrifugal paths of the 

 vagus, and possibly also by way of the sympathetic. 



(f) Other observations show that after the secretion from the 

 sac has been started by the stimulus of peptone, it increases 

 considerably when egg-albumin is introduced into the stomach, 

 though this by itself is ineffective. 



(g) The gastric secretion excited by the presence of food in the 

 stomach reaches its maximum in the first and second hours (after 

 ingestion of milk only in the third hour). After that it gradually 

 diminishes, and then ceases entirely. For any given kind of 



