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PHYSIOLOGY OF DIGESTION AND SECRETION. 



for examination. Formerly a silver cannula was placed in the 

 fistula, and at any time the plug closing the cannula might be re- 

 moved and gastric juice be obtained. In some cases the esophagus 

 has been occluded or excised so as to prevent the mixture of saliva 

 with the gastric juice. Gastric juice may be obtained from human 

 beings also in cases of vomiting or by means of the stomach tube, 

 but in such cases it is necessarily more or less diluted or mixed with 

 food and cannot be used for exact analyses, although specimens 

 of gastric juice obtained by these methods are employed in the 

 diagnosis and treatment of gastric troubles. 



From the standpoint of experimental investigation a very im- 

 portant addition to our methods was made by Heidenhain. This 

 observer showed that a portion of the stomach the fundic end, for 

 instance, or the pyloric end might be cut away from the rest of the 



organ and be given an 

 artificial opening to the 

 exterior. By this means 

 the secretion of an isolated 

 fundic or pyloric sac may 

 be obtained and examined 

 as to its quantity and prop- 

 erties. The method was 

 subsequently improved by 

 Pawlow, whose important 

 contributions are referred 

 to below. Fig. 270 gives 

 an idea of the operation as 

 made by Pawlow to isolate 

 a fundic sac with its blood 

 and nerve supply unin- 

 jured. 



The normal gastric se- 

 cretion is a thin, colorless 

 or nearly colorless liquid 

 with a strong acid reaction and a characteristic odor. Its spe- 

 cific gravity varies, but it is never great, the average being about 

 1.002 to 1.003. Upon analysis the gastric juice is found to contain 

 a trace of protein, probably a peptone, some mucin, and inorganic 

 salts, but the essential constituents are an acid (HC1) and two 

 enzymes, pepsin and rennin. Satisfactory complete analyses of the 

 human juice have not been reported, most of the recent observers 

 confining their attention mainly to the degree of acidity and digestive 

 power. Gastric juice does not give a coagulum upon boiling, but the 

 digestive enzymes are thereby destroyed. One of the interesting 

 facts about this secretion is the way in which it withstands putrefac- 

 tion. It may be kept for a long time, for months even, without 



Fig. 270. To show Pawlow's operation for 

 making an isolated fundic sac from the stomach: 

 v, Cavity of the stomach ; , the fundic sac, shut off 

 from the stomach and opening at the abdominal 

 wall, a, a; b indicates the line of sutures. (Paw- 

 low.) 



