PEPSIN. 33 1 
equal amounts of pepsin: the pyloric cud always contains much less 
than the fundus or bhe 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 cm 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 < !. 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, ami 
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 0° 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 he 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 T6 per- 
cent. 
Supposed compound of pepsin and hydrochloric arid. — 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, Jakresb. it. cl. FortscJir. d. Thicr-Chem., Wiesbaden, 1S72, 
Bd. ii. S. 210 ; 1873, Bd. iii. S. 169 ; 1874, Bd. iv. S. 236 ; Klemensiewic-z, 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 Biernaeki, Ztschr. f. Biol., Munchen, 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. /'. Biol., Miinchen, 1892, Bd. xxviii. S. 453. 
5 Maly, Hermann's " Handbuch," Bd. v. (2) S. 73. 
6 Sitzungsb. d. h. Akad. cl. Wissoisch., Wien, 1859, Bd. xxxvii. 8. 131 ; Hammarsten 
gives for fibrin O'Stol ; for myosin, casein, and vegetable proteid. 1 ; for hard-boiled proteid, 
2-5 parts per litre. — " Lehrbuch," Anil. 3, S. 238. 
