206 DIGESTION. [CHAP. xxiv. 



Lehmann attributes the acidity of the gastric fluid to both free 

 hydrochloric and lactic acids. He obtained the former from the 

 stomach of a diabetic patient, to whom he had administered an 

 ipecacuanha emetic ; and the latter from the stomach of a cat, from 

 which he was able to procure distinct crystals of lactate of zinc. 

 In subsequent researches, Lehmann confirmed this conclusion 

 respecting the nature of the acid of the gastric fluid. 



Liebig lends his sanction to this doctrine, and especially to the 

 view put forward by Bernard and Barreswil, that both lactic and 

 phosphoric acids exist in this fluid free, while there is no reason to 

 deny the existence of an acid phosphate likewise. The opinion 

 that free lactic acid exists in the gastric fluid is not new. It was 

 put forward by Chevreul many years ago, and afterwards by 

 Leuret and Lassaigne. In 1823, our distinguished friend, Dr. 

 Graves, of Dublin, published analyses of the fluid of the stomach 

 from two patients, in which he found free lactic acid in abundance. 

 Notwithstanding what has been done on this subject, it must be con- 

 fessed that the full truth has scarcely yet been arrived at. We 

 have yet to learn whether the constitution of the gastric juice is 

 constant whether the same acids or acidifying agents are present 

 in all animals, and under all conditions of feeding and food ; and 

 we have also to ascertain whether any and what changes may be 

 produced by disease in the chemical characters of the gastric fluid. 

 The enquiry, taken up on a large scale among the lower animals, 

 and extended to man, in health and disease, would, no doubt, 

 yield most valuable and interesting results. 



The digestive principle does not seem to be secreted in equal 

 quantity or of equal power at all parts of the stomach. Meat and 

 albumen, digested with mucous membrane from the cardia, is by no 

 means so much acted upon as if digested with mucous membrane 

 from the pylorus or from the central part of the stomach. In the 

 pig there is a large patch of the membrane of a reddish hue, and of 

 considerable thickness, forming that portion of the mucous membrane 

 which corresponds to the middle of the great curvature of the 

 stomach ; this, we find, exercises a more energetic action upon meat 

 or albumen than any other part. 



It is highly interesting to notice that the mucus which accumu- 

 lates upon the surface of the mucous membrane of the stomach has 

 a digesting power corresponding to that of the portion of mucous . 

 membrane from which it has beeu taken. This we have deter- 

 mined by our own experiments. 



Nature of the Digesting Power of the Gastric Juice. Having 



