336 



STOMACH AND INTESTINE. 



constituents. It was reserved for Mialhe* to 

 show, that the homogeneous physical con- 

 stitution, which the whole contents of the 

 stomach were erroneously supposed to assume 

 at the end of its digestive act, is true in a 

 much more important chemical sense, if limited 

 to certain portions of the food. He found 

 that the gastric digestion of the various protein 

 compounds affords a solution which, what- 

 ever the nature of the substance originally 

 dissolved, possesses the same physical and 

 chemical properties : these properties being 

 due to its containing a substance which, 

 from its relations to albumen, he called 

 albuminose. Lehmann -j-, who has confirmed 

 and extended Mialhe's researches, proposes 

 for this substance the better name of 

 peptone. J 



Peptone. According to these observers, the 

 following properties are common to all kinds 

 of peptone, from whatever substances they 

 may have been derived. Reduced to the solid 

 form by careful evaporation, peptone is a white 

 or yellowish- white substance ; almost tasteless 

 and inodorous ; very soluble in water ; but inso- 

 luble in alcohol of 83 per cent. Its watery 

 solution reddens litmus; and is precipitated 

 by chlorine, tannic acid, and metallic salts ; 

 but is unaffected by boiling, by acids, or by 

 alkalies. With alkalies and bases it forms 

 very soluble neutral compounds or salts. An 

 aqueous solution of these is still less preci- 

 pitable by reagents than one of peptone itself. 

 Thus it is thrown down only by tannic acid, 

 bichloride of mercury, and a mixture of the 

 acetates of ammonia and lead : the acetate 

 of lead, and the ferrocyanide of potassium 

 causing but a faint cloudiness; and even con- 

 centrated acids, nitrate of silver, and alum, 

 having no effect. 



The ultimate chemical composition of any 

 particular peptone so closely resembles that 

 of the substance from which it is formed as 

 scarcely to require any further remark. 



In speaking of these chemical phenomena 

 of stomach-digestion, there remains but to 

 notice, that the addition of water, or a small 

 quantity of fresh acid, is capable of re- 

 storing some of its original digestive powers 

 to saturated gastric juice, or a solution of 

 peptone. The degree in which this renovation 

 can be effected is obviously a question of great 

 importance. But at present there are no 

 exact observations on which to found any 

 conjectures respecting it. It seems, however, 

 sufficient to explain the discrepancy previously 

 alluded to$ between the quantity of hydro- 

 chloric acid which is present in the normal gas- 

 tric juice, and that which is required to be 



* Journal de Pharmacie, t. x., pp. 161. et sea 



t Op. cit. vol. ii. p. 50. 



j Both names being comparatively recent, there 

 can be little objection to the adoption of the prefer- 

 able one. And "peptone" not only connotes its 

 relation to digestion, but avoids the disadvantage 

 of "albuminose": viz., that of giving an undue 

 prominence to the connection of albumen with the 

 gastric function. 



See p. 334. 



added in preparing an artificial digestive fluid 

 of maximum solvent power. 



The foregoing brief summary of the chief 

 physical and chemical properties of the gastric 

 juice, naturally leads us to the important 

 question What is the nature of its action? 



1. It is obvious that the phenomena of 

 gastric digestion do not constitute a simple 

 process of solution by a dilute acid. For the 

 organic principle is essential. The substances 

 are not merely dissolved, but exhibit altered 

 reactions. And, finally, they are not restored 

 to their original form by the neutralization of 

 the acid. 



2. Some have supposed that the organic 

 principle exercises a contactive influence, like 

 that of spongy platinum in the acetification of 

 alcohol. 



3. Others have imagined that it produces a 

 fermentation, like that excited by yeast in a 

 solution of sugar. 



But we have seen that gastric juice will 

 not dissolve more than a certain quantity of 

 protein-compounds. While, in both of the 

 above processes, a small quantity of the con- 

 tactive or fermenting substance excites an 

 action, which continues until the whole mass 

 has been oxidized or fermented, as the case 

 may be. This objection appears fatal to both 

 these theories. And as regards the latter ol 

 them, we may further point out, that, unlike 

 the particles of yeast, which are themselves 

 undergoing metamorphosis, those of the di- 

 gestive fluid are singularly stable, and enjoy 

 a singular immunity from the putrefactive 

 process. 



4. Schmidt* has propounded a fourth 

 theory, according to which the organic prin- 

 ciple, and the acid, of the gastric juice are 

 united to each other in the form of a complex 

 acid, which he calls the hydrochloro-pepsic. 

 This is decomposed by heat into pepsine and 

 hydrochloric acid. In the stomach it unites 

 with protein-compounds as bases, to form so- 

 luble combinations. When treated with an 

 alkali its pepsine is precipitated. And even 

 when saturated with a protein-compound the 

 power of the gastric juice is restored by fresh 

 acid; because the latter, by uniting with the 

 base, sets free the hydrochloro-pepsic acid, 

 and thus enables it to combine with another 

 portion of proteinous substance. 



But in respect to the two latter statements, 

 it would appear that an alkali precipitates from 

 the gastric juice but a very small part of its 

 pepsine; and that even this portion is in com- 

 bination with calcareous salts. While the re- 

 actions of peptone show that the original 

 pepsine is neither present as such, nor is ca- 

 pable of being set free from its state of com- 

 bination by the addition of an acid. 



And other facts, which seem to speak strongly 

 in favour of this view, will as little bear a close 

 investigation. Such are the close union of the 

 acid to the organic principle; the definite 

 amount of acid required for artificial digestion ; 

 and the similarly definite amount of proteinous 



* Loc. cit. 



