THE DIGESTIVE SECRETIONS 923 



for 24 hours, drying it, pulverizing it and extracting it in glycerin for 

 6 or 7 days. On addition of alcohol to the filtrate, the pepsin is 

 precipitated, which may then be added to dilute hydrochloric acid. 

 The Characteristics of Gastric Juice. — When obtained from a 

 fasting animal, gastric juice is quite clear, odorless, acid in reaction, 

 and sour to the taste. Its specific gravity varies between 1.002 and 

 1.006 and its depression of the freezing point between 0.47° and 

 0.65° C.^ Its quantity may be considerable, large dogs yielding 

 as much as 1 liter in the course of 3 hours. Human subjects secrete 

 700 c.c. during a moderate meal and an average total per day of 1500 

 c.c. As Carlson^ has pointed out, the gastric glands of a healthy 

 person are never wholly dormant, but secrete continuously in amounts 

 varying between 2 and 50 c.c. in an hour; the higher figures, however, 

 are exceptional. Gastric juice contains only 0.3 to 0.6 per cent, of 

 total solids, as follows: 



Acid. 0.46-0.58 per cent. 



Chlorin . 49-0 . 62 per cent. 



Total solids . 43-0 . 60 per cent. 



■ Ash 0.06-0.16 per cent. 



If gastric juice is cooled and is allowed to stand, it becomes cloudy and gives rise 

 to a deposit of finely granular and highly refracting material which appears to 

 consist of the active principle pepsin. This agent unfolds its action only in an acid 

 medium which is supplied to it by the hydrochloric add (Prout, 1824). Since the 

 latter is present in amounts varying, in dogs, between 0.45 and 0.58 per cent, and, 

 in man, between 0.25 and 0.35 per cent., about 3 grams of hydrochloric acid 

 must be produced at each meal. In some persons, however, there may be an 

 achlorhydria or absence of hydrochloric acid, although some peptic digestion may 

 still be present. A condition of this kind constitutes a diagnostic sign of consider- 

 able value. It commonly develops in the course of carcinoma of the stomach. 

 The reverse condition is hyperchlorhydria, which is usually associated with a 

 hyperpeptic activity and a deficiency in mucus. The cause of this excess in acid 

 usually lies in a hyperirritability of the nervous system, as well as in lesions produc- 

 ing a constant stimulation of the gastric mucosa, such as ulcers and growths else- 

 where in the abdominal cavity. 



The acidity of the gastric juice is usually ascertained by means of a test break- 

 fast. When only a light evening meal is taken, the stomach should be empty 

 in the morning, i.e., after a period of rest of about 12 hours. The breakfast should 

 consist of a roll or five crackers or biscuits and a cup of weak tea. A sample of 

 gastric juice is obtained 45 minutes later by means of the stomach tube. While 

 the analytical procedures to be followed in this case cannot be described in detail 

 in a book of this kind, it might be mentioned that the unfiltered juice may be ti- 

 trated with N/10 NaOH, using phenolphthalein as an indicator. Although the 

 determination of the free hydrochloric acid may be made with Gtinzberg's or Toper's 

 reagent, 3 the most accurate procedure is to ascertain the number of hydrogen ions 

 in the juice in accordance with the gas-chain method.^ The former reagent con- 



^ Rosemann, Pfliiger's Archiv, cxviii, 1907. 467, and Sommerfeld, Archiv fiir 

 Physiol., 1905, 455. 



2 Am. Jour, of Physiol., xxxvii, 1915, 50. 



3 Zeitschr. fiir physiol. Chemie, xix, 1894, 104 ; also : Christianson, Bioch. 

 Zeitschr., xlvi, 1912, 24. 



^ Panton and Tidy, Analysis of Gastric Contents, Quart. Jour, of Medicine, iv, 

 1910-1911. 



