58 GASTRIC JUICE. 



another part of this work ; this much, however, may be concluded 

 with certainty, that the digestion of the protein-compounds is some- 

 thing more than a simple formation of the well-known hydrochlorate 

 of albumen, as was formerly supposed, and as has partly been 

 assumed by Schmidt, in the hypothesis to which we have pre- 

 viously referred. 



The following facts are worthy of notice in reference to the 

 digestive power of the gastric juice : it is suspended by boiling, by 

 saturating the free acid with an alkali or even with phosphate of 

 lime, by sulphurous, arsenious, and tannic acids, by alum and by 

 most metallic salts ; and it is very much impeded by the addition 

 of alkaline salts, or by saturating the fluid with peptones or other 

 organic substances, either nitrogenous or non-nitrogenous. The 

 addition of water to a gastric juice which has been already saturated 

 by a peptone, enables it to digest an additional quantity of protein- 

 substances ; the digestive power is also restored to a certain degree 

 by the repeated addition of free acid. Too much free acid with- 

 out due dilution with water, entirely suspends the digestive power. 

 The most favourable ratio of the free acid of the gastric juice is 

 when 100 parts of the latter are saturated by about 1*25 of potash. 

 Hydrochloric and lactic acids are the only acids which yield 

 energetic, active digestive fluids with pepsin ; sulphuric, nitric, and 

 acetic acids yield with pepsin a digestive mixture of only slight 

 power ; while phosphoric, oxalic, tartaric, and succinic acids can in 

 no degree replace the lactic or hydrochloric acid in the process of 

 digestion. Fats, when added in certain quantities to the gastric 

 juice, promote the conversion of the protein-compounds into 

 peptones. 



It need excite no wonder that sulphurous, arsenious, or tannic 

 acid should suspend the digestive power of the gastric juice, for it 

 is well known that these substances check other metamorphoses, 

 and especially the phenomena of fermentation. Taking into con- 

 sideration the chemical properties of pepsin, and its power of 

 combining with metallic salts and other substances, we could 

 hardly expect that the above-named substances would exert any 

 other effect on the digestive power of the gastric juice. 



Wasmann has very clearly shown that no digestion is possible 

 unless the gastric juice contains a free acid ; indeed he was led to 

 the view that the digestive power resides " in solo acido." This 

 latter view is, however, sufficiently controverted by the experiments 

 of numerous observers ; we need, for instance, only refer to those 

 of Blondlot, who believed that he had shown that the peptones are 



