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37 



VIII 

 GASTRIC DIGESTION 



120. The gastric juice, secreted by the glands of the 

 stomach, differs from the other digestive fluids in having an 

 acid reaction. It is a clear thin liquid having a specific 

 gravity of 1002-1006. The average composition of man's gas- 

 tric juice is as follows : 



Water 99.26 



Pepsin rennin and other organic matter 0.30 



Free hydrochloric acid 0.22 



Alkali chlorides 0.20 



Phosphates of alkalies, 



calcium, magnesium and iron 0.02 



There is more hydrochloric acid than can unite with the 

 bases, and this must consequently be in the free state. The 

 most important of the organic substances are the two enzymes: 

 pepsin and rennin. Differences exist in different animals, e.g., 

 in carnivora there is' a higher percentage of acid than in 

 others. 



An artificial digestive fluid giving very good results may 

 be made by dissolving 0.3 gram of commercial pepsin in 1000 

 cc. of a 0.2% solution of hydrochloric acid. 



It is more desirable in many ways, however, to prepare an 

 extract from the gastric mucous membrane itself. The writer 

 has found the following method to answer very satisfactorily. 

 To each gram of the mucous membrane add 1 cc. of a 1% 

 solution of acetic acid. Triturate thoroughly in the mortar ; 

 then add 10 cc. of chloroform water for each gram of the 

 mucous membrane. This may be kept for some time. When 

 ready to use, filter and ad(^ 2 cc. of the extract to 8 cc. of the 

 0.2% hydrochloric acid, or equal volumes of the extract and 

 the acid may be used. 



From a comparative stand point, extracts may be made 

 from each of the three great groups of animals : Oni'hivora 

 (pig), carnivora (dog), and herbivora (horse or cow), and 

 differences in the rate of digestion noted. 



121. Label 6 test tubes. A, B, C, D, E, F. In A fill the 

 tube half full of distilled water, and add 30 drops, or 2 cc. of 



