334 



STOMACH AND INTESTINE. 



ive fluid will, however, sustain a temperature 

 of 160 without damage. But at a heat above 

 this, it becomes wholly inactive, and partially 

 insoluble. And Dunglison* found the organic 

 principle of the gastric juice to be insoluble in 

 hot water. 



Alcohol, acids, and alkalies, when applied 

 in excess, have also a destructive influence on 

 the digestive power of pepsine. 



In the case of acids, this injurious effect is 

 much less marked. As might have been ex- 

 pected from the constant reaction of the gas- 

 tric juice, an acid is essential to its digestive 

 efficacy ; indeed, we might almost say, to its 

 very existence. Even that incomplete loss of 

 acid, which we have seen to be involved in the 

 precipitation of its pepsine, must be compen- 

 sated by an artificial acidulation, before the 

 aqueous solution of this substance regains its 

 former digestive powers. 



Here, however, as in the case of heat, it is 

 necessary that certain limits should be obser- 

 ved. Wasmann found that an addition of 

 about 3 parts of hydrochloric acid per 1000 

 formed a tolerably effective fluid: a quan- 

 tity which corresponds with about half of 

 that present in the gastric juice according 

 to Bidder and Schmidt's analyses.-}- But 

 much larger proportions of this acid may be 

 added, not only with impunity, but even with 

 advantage. Thus Schwann used from 6 to 

 12 parts per 1000. And Elsaesser thinks 

 that the most favourable proportion for diges- 

 tive purposes is about 3 or 4 per cent, of 

 muriatic acid : a quantity which would be 

 about five times as great as that present in the 

 gastric juice. 



But the nature of the acid seems a matter 

 of indifference. J Nitric, phosphoric, sulphu- 

 ric, acetic, and lactic acid, have all been suc- 

 cessfully made use of. And the range of amount 

 already specified for hydrochloric acid might, 

 a priori, prepare us for the fact, that the re- 

 quisite quantities of each of these acids seem 

 solely related to their more or less dilute state; 

 and do not allow us to recognize any trace of 

 an equivalent chemical proportion. 



Applied in still larger quantities, all of these 

 acids first weaken, and then destroy, the 

 digestive power of the solution of pepsine. 

 The comparative amount of injury inflicted by 

 equal quantities of the different acids appears 

 to depend, like their solvent efficacy, chiefly 

 on the degree of their concentration, and that 

 of the digestive fluid itself. 



How essential its acid is to the solvent 

 powers of a natural or i artificial gastric juice, 

 is well shown by the effect of neutralizing it 

 with an alkali. Under these circumstances, 

 not only does it lose all action upon albu- 

 minous substances, but if mixed with them, 

 soon shares in the putrefaction which they 

 are liable to undergo. An equally rapid putre- 

 faction occurs in the simple aqueous infusion 



- * Beaumont, Op. dt. p. 69. 



t The acid Wasmann added to the pepsinous 

 fluid being liquid, would contain less than half its 

 weight of true hydrochloric acid. 



J Bernard, Loc. cit. ; Lehmann, vol. ii. p. 50. 



of stomach. Left to itself, however, the 

 powers of the neutralized gastric juice are only 

 suspended ; and can be restored by the addi- 

 tion of a proper quantity of acid. But in the 

 course of time, the neutral fluid gradually 

 becomes mouldy : a process which appears 

 to differ in its rapidity only from the similar 

 decomposition that occurs in pure gastric 

 juice, apparently after the slow evapora- 

 tion of its acid.* A still larger quantity of 

 alkali permanently destroys all its solvent 

 powers, and is followed by its rapid putrefac- 

 tion. 



That incomplete loss of acid which was 

 noticed as occurring in the ordinary processes 

 for obtaining pepsine, does not entirely sus- 

 pend its specific action. On the contrary, its 

 watery solution still retains the power of pre- 

 cipitating large quantities of casein, and even 

 of exerting a feeble digestive or solvent influ- 

 ence. 



But while all such observations on the 

 artificial digestive fluid agree in representing 

 an acid as one of its most essential elements, 

 some physiologists have gone further, and have 

 asserted it to be so far the true and only prin- 

 ciple of the gastric secretion, as to be capable 

 of imitating its action. And others, who 

 allow that the dilute acid is only rendered 

 efficacious by the presence of the organic 

 matters with which it is combined, have 

 doubted the specific nature of the gastric prin- 

 ciple; and have asserted that acidulated saliva 

 or mucus, or an acidulated infusion of blad- 

 der, diaphragm, trachea, or intestine, is ca- 

 pable of effecting a solution of the protein com- 

 pounds like that seen in artificial digestion. 

 Each of these remarkable statements demands 

 a passing notice. 



Many dilute acids such as sulphuric, nitric, 

 acetic, hydrochloric, and phosphoric can 

 certainly produce appearances resembling 

 imperfect solution, in meat and many of the 

 protein compounds. But such a solvent ac- 

 tion, even when most marked as in the 

 steeping of small pieces of coagulated albu- 

 men in dilute hydrochloric or phosphoric acid 

 differs greatly, both in nature and amount, 

 from the true stomach digestion. It requires 

 the aid of a much higher temperature ; it is ex- 

 cessively slow, superficial, and imperfect ; and 

 the resulting weak and turbid solution often 

 parts with its dissolved constituents on the 

 addition of the ordinary reagents. 



The same statement will apply to various 

 experiments that have been made with an aci- 

 dulated infusion of large or small intestine; in 

 which the process of solution, though some- 

 what f more energetic, is still so feeble, slow, 

 and imperfect J, as to be scarcely comparable 

 with that effected by the gastric juice. While 

 we ought not to forget, that the superior 



* Beaumont, Op. cit. p. 71. ; Blondlot, Op. cit. p. 

 351. 



f Compare Valentin, vol. i. p. 366. ; Todd and 

 Bowman, vol. ii. p. 203. ; and Frerichs, p. 795. 



J In any future observations of this kind it 

 would be very desirable to institute a strict com- 

 parison between the reactions of the resulting solu- 

 tion, and those of true peptone or albuminose. 



