PHYSIOLOGICAL CHEMISTRY 379 



as digestion proceeds, because the combining power of the proteoses 

 and peptones for hydrochloric acid is greater than that of native 

 protein. In consequence of this increasing absorption of hydrochloric 

 acid during peptic digestion, the acid becomes combined as soon as it is 

 secreted for some considerable time after the start of digestion. After 

 a test meal of soup, meat (200 gr.) and bread (50 gr.) it takes from 

 three to four hours before there conies to be any free hydrochloric acid 

 detectable in the gastric contents, although during all this time the 

 acid is being actively secreted. In cancer and in catarrhal conditions 

 of the gastric mucosa, and in fever, the secretion of hydrochloric acid is 

 depressed so that it may all become combined with protein and never 

 appear in the free state, i.e. never come to react with the above 

 indicators. 



2. To prevent putrefaction in the stomach. Hydrochloric acid in 

 the free state, like any other mineral acid, is a strong antiseptic. The 

 micro-organisms with which our food is contaminated are therefore 

 destroyed before they have had time to multiply to any degree in the 

 stomach. If it were not for this, the stomach contents would serve as 

 a most favourable place for the growth of these micro-organisms, and 

 putrefaction and fermentation would become excessive in them. This 

 is -actually what occurs when the secretion of hydrochloric acid is 

 deficient, as in cancer. If, in such cases, the reaction of the stomach 

 contents be tested, it will nevertheless be found strongly acid to litmus, 

 and if, furthermore, the degree of this acidity be estimated (by the 

 method described on page 381), it may be- found even higher than that 

 of normal gastric contents. By the application of the indicator tests 

 described above (especially Giinzberg's), it can readily be shown that 

 the acidity is not due to free hydrochloric acid. This leaves, as its 

 possible causes, hydrochloric acid combined with protein, acid salts, and 

 organic acids. Since it is known that micro-organismal growth is apt 

 to produce organic acids, especially lactic acid, we next proceed to test 

 for the presence of this. 



EXPERIMENT V. The test for lactic acid is performed with an ethereal 

 extract of the gastric contents, which is made by mixing 5 c.c. of the 

 gastric contents with 30 c.c. ether in a separating funnel, then gently 

 shaking the two with a rotatory motion (avoid violent shaking, else an 

 emulsion is apt to occur), and, after settling, pouring off the ether. 

 The ethereal extract is then evaporated to dryness, 1 the residue dis- 

 solved in a little water, and the resulting solution tested with Uffel- 



1 In evaporating ether, be very careful that no flame is near. The evaporation 

 should be performed on a water bath that has been heated, and the flame then 

 extinguished. 



