332 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



addition of hydrochloric acid, because the compound is not re-formed, 

 meets a simple answer in the statement that the pepsin is permanently 

 destroyed by the strong acid or alkali used. A strong argument against 

 any such compound is that the concentrations of different acids causing 

 equal activity in pepsin are not proportional to the chemical equivalents 

 of the acids, as might be expected if the acids entered into chemical 

 combination with the pepsin. 1 



Pepsin is very rapidly destroyed by solutions of alkalies or alkaline 

 salts. 2 The principal conditions which influence the rate of destruction 

 of pepsin by sodium carbonate are the strength of the solution of the 

 alkaline salt, the time during which it is allowed to act, the temperature 

 of the mixture, and the amount of proteid present. The mere act of 

 neutralising an acid pepsin solution may destroy a considerable part of 

 the pepsin. When equal volumes of a fluid containing pepsin and of a 

 1 per cent, solution of sodium carbonate are well mixed, the greater part 

 of the pepsin is destroyed in fifteen seconds ; in a neutralised acid 

 extract of the gastric mucous membrane of a cat, the amount thus 

 destroyed may be JJ of the whole. Even very dilute sodium carbonate 

 (005 per cent.) will cause an appreciable destruction of pepsin in one 

 or two hours at the body temperature, provided proteids are present 

 in small amount only. 



Proteids lessen the rate of destruction of pepsin, probably by 

 combining with the alkali or alkaline salts, for the greater the amount 

 of sodium carbonate present the greater must be the amount of proteid 

 to lessen appreciably the destruction. In the presence of -5 per cent, 

 sodium carbonate, less than -25 per cent, of peptone has very little effect, 

 and even 2*5 per cent, of peptone does not prevent the greater part of the 

 pepsin from being destroyed. Thus, in the presence of 2'5 per cent, 

 peptone, seven-eighths of the pepsin in an extract of a cat's gastric 

 mucous membrane may be destroyed at 17 C. by -5 per cent, sodium 

 carbonate in sixty seconds. Pepsin prepared from a frog is less rapidly 

 destroyed than pepsin prepared from a mammal. Carbonic acid destroys 

 pepsin also, but less rapidly than it destroys pepsinogen. 3 



Solutions of salts of the heavy metals weaken or entirely remove the 

 activity of pepsin solutions, according to the amount added. This effect 

 is probably due to the enzyme being mechanically carried down in the 

 usual fashion by the precipitate formed between heavy metal and pro- 

 teid. The neutral salts of the alkalies and alkaline earths, when added 

 (even in small quantity) to solutions of pepsin, decrease the activity. 

 Thus Al. Schmidt 4 found that salt-free proteid dissolved in a few seconds 

 in salt-free pepsin solution, but on the addition of 0'5-0'G per cent, of 

 sodium chloride the time of solution was increased three to ten times. 

 Hydrobromic and hydriodic acids in large doses, and to a still greater 

 extent their potassium salts, delay peptic digestion. Sulphurous acid stops 

 peptic digestion, but arsenious and hydrocyanic acids, except in large 

 amounts, have little effect. Carbolic acid in small quantities has also 

 little effect, but acts injuriously in greater concentration. Salicylic acid 



1 Davidson n. Dietrich, Arch. f. Anat. u. PhysioL, Leipzig, 1860, S. 688 ; Putzeys, 

 Jahresb. it. d. Fortschr. d. Thier-Chem., Wiesbaden,' 1877, Bd. vii. S. 279; Halm, Virchow's 

 Archiv, 1894, Bd. cxxxvii. S. 597. 



a Langley, Journ. Physiol., Cambridge and London, 1882, vol. iii. pp. 253, 283 ; 

 Langley and Edkins, ibid., 1886, vol. vii. p. 371. 



3 Quoted from Langley and Edkins, loc. cit. 



4 Jahresb. u. d. Fortschr. d. Thier-Chem., Wiesbaden, 1876, Bd. vi. S. 23. 



