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composition, a saline solution not only fails to evoke it, but injures 

 or destroys the gastric powers. 



There is no evidence of any exhaustion of the pepsinous consti- 

 tuents of the gastric mucous membrane at any period of digestion. 



As regards other variations of power, age seems to exercise but a 

 moderate influence on the gastric mucous membrane ; species, again, 

 has a subordinate effect ; genus is much more influential. For units 

 of mucous membrane, Fishes seem to have the most powerful gastric 

 digestion. 



The influences of temperature, analogous in all animals, vary 

 exceedingly as regards the absolute heats which respectively favour, 

 accelerate, and destroy the powers of the stomach ; so that the same 

 heat which is practically necessary for the function of this organ in 

 a warm-blooded Mammal, annihilates the efficacy of the pepsine of 

 many Fishes. 



The action of the gastric juice is a transfer, to albumen, &c., of a 

 molecular change going on in the gastric juice ; pepsine and pep- 

 tone being essentially analogous to each other in properties. 



The formation of peptone is a hydration of albumen, as shown 

 by various collateral circumstances of the process. 



ADDENDA. 



1 . The pancreatic juice, or pancreatic infusion, which converts 

 albumen into a substance akin to peptone, and in proportions not very 

 unlike those which would be obtainable by using certain parts of the 

 mucous membrane of the stomach of some animals, and which does 

 this by a process so far sui generis, as that it is no way shared by the 

 salivary organs most analogous to itself in structure and function, 

 is yet distinguishable from the gastric juice in regard to the process 

 and the product of this change. The change is, indeed, an incident 

 of putrefaction only, and therefore not a function of the healthy living 

 organ. 



2. The intestinal juice, or the secretion of the intestinal tubes, is 

 neither capable of converting albumen, &c. into peptone, nor of con- 

 verting starch into sugar. The offices of these tubes are therefore, 

 probably, chiefly of absorption and of excretion. 



