PEPSIN. 331 



equal amounts of pepsin: the pyloric end always contains much less 

 than the fundus or the cardiac end, but is never quite devoid of pepsin. 

 It was formerly held by some observers that the pepsin found in the 

 pyloric end was due to infiltration by the secretion from the glands of 

 the remainder of the stomach, but the secretion obtained from pyloric 

 fistulse contains pepsin which can only be secreted by the glands of this 

 region of the stomach. 1 



Effects of temperature. Pepsin in neutral solution is destroyed by a 

 temperature of 55 C. ; in a solution containing two parts per thousand 

 of hydrochloric acid it is not destroyed at this temperature, but is 

 destroyed in five minutes at a temperature of 65 C. By the addition 

 of peptones or certain salts it is so protected that it is only destroyed 

 in an equal time by a temperature of 60 C. 2 According to v. Wittich, 3 

 the maximum rapidity of action is found between 35 and 50 C., and 

 the rapidity of destruction by elevated temperature (as in the case of 

 ptyalin) is dependent on the amount of dilution of the ferment, and the 

 duration of the high temperature. The more dilute the pepsin solution 

 the more quickly it is destroyed, and the lower the limit of temperature 

 necessary. Pepsin is still faintly active at C. 4 



Effects of reaction. Pepsin is only active in acid solution ; the most 

 effective acid is hydrochloric acid, but other acids are also capable of 

 setting it in action in varying degree. The most energetic of the other 

 acids are nitric, lactic, and phosphoric, followed at some distance by 

 sulphuric, acetic, oxalic, and tartaric acids. The most effective acids 

 seem also to be those which most easily swell up fibrin. Acid sodium 

 phosphate does not confer activity on pepsin. 5 



The amount of acidity required for optimum activity varies greatly 

 with the form of proteid to be digested; thus Briicke 6 gives for 

 fresh fibrin '08 per cent., but for heat-coagulated fibrin '12 to *16 per 

 cent. 



Supposed compound of pepsin and hydrochloric acid. The hypothesis 

 has been put forward, that the pepsin and hydrochloric acid in gastric 

 juice are united to form a loose compound " pepsin - hydrochloric 

 acid." 



There is no clear evidence in favour of the existence of such a 

 compound. It is said to be precipitated from gastric juice by the 

 soluble salts of lead and mercury, and to be re-obtainable unaltered 

 from the precipitate by decomposing with sulphuretted hydrogen. But 

 it is certain that both the acid and pepsin would be thrown down by 

 such salts, and there is no reason to suppose that they are not thrown 

 down separately instead of as a compound, and recovered together again 

 on decomposing the mixed precipitate. A second argument, that the 

 supposed compound acid can be decomposed by strong acids or alkalies, 

 and that the pepsin so separated does not again become active on the 



1 See Ebstein and Griitzner, Jahresb. it. d. Fortschr. d. Thier-Chem., Wiesbaden, 1872, 

 Bd. ii. S. 210 ; 1873, Bd. iii. S. 169 ; 1874, Bd. iv. S. 236 ; Klemensiewicz, ibid., 1875, 

 Bd. v. S. 162; Heidenhain, ibid., 1878, Bd. viii. S. 245 ; King, ibid., 1894, Bd. xxiv. 

 S. 334; Akermann, Skandin. Arch. f. Physiol., Leipzig, 1895, Bd. v. S. 134. 



2 Biernacki, Ztschr. f. BioL, Miinchen, 1892, Bd. xxviii. S. 49. 



3 Arch.f. d. ges. Physiol., Bonn, 1869, Bd. ii. S. 193 ; 1870, Bd. iii. S. 339. 



4 Flaum, Ztschr. f. BioL, Miinchen, 1892, Bd. xxviii. S. 453. 



5 Maly, Hermann's " Handbuch," Bd. v. (2) S. 73. 



6 Sitzungsb. d. k. Akad. cl. Wissensch., Wien, 1859, Bd. xxxvii. S. 131 ; Hammarsten 

 gives for fibrin 0'8 to 1 ; for myosin, casein, and vegetable proteid, 1 ; for hard-boiled proteid, 

 2-5 parts per litre. " Lehrbuch," Aufl. 3, S. 238. 



