446 PRACTICAL PHYSIOLOGY 



or the Tropaeolin test does not exclude the presence of a trace of 

 hydrochloric acid, as peptone, etc., may mask the reaction. If the 

 reactions be positive, however, the presence of free hydrochloric acid 

 may be assumed. 



Tests for Organic Acids (lactic, acetic, and butyric). As explained 

 above, these acids become developed when there is a deficiency of 

 hydrochloric acid in the gastric juice, for then micro-organisms grow 

 in the gastric contents, and, by their action on the food-stuffs, lead 

 to the production of organic acids. 



In order to test for them, it is best to extract the gastric contents 

 (vomit) with ether. For this purpose shake up about 20 c.c. of 

 the fluid with about five times its bulk of ether in a separating 

 funnel as described on p. 492. Eemove the ethereal extract, and 

 divide it into two portions A and B ; place each portion in a porcelain 

 basin. Allow B to stand exposed to the air, and place A on a warmed 

 water bath. After the ether has evaporated in A, dissolve the residue 

 in water and apply Uffelmann's reaction (see p. 188) a positive 

 result indicates lactic acid. When the ether has evaporated from 

 B, dissolve the residue in water and divide the resulting solution into 

 two parts. Neutralise one of these with sodium carbonate, and add 

 a drop of a very dilute solution of ferric chloride the red colour 

 indicates the presence of acetic acid. To the other part add a small 

 fragment of calcium chloride. If oily drops appear on the surface 

 butyric acid is present. Since both these acids in B are volatile, they 

 would be driven off unless the ether had been evaporated at low 

 temperature. 



Estimation of Total Acidity of Gastric Contents. A measured 

 quantity (10 c.c.) of filtered gastric contents is mixed in an Eiien- 

 meyer's flask with ten times its bulk of distilled water. Two or three 

 drops of a solution of phenol-phthalein are added, and the solution is 

 titrated with n/W sodium hydrate solution (see page 245) until a 

 permanent pink colour is just obtained. The number of c.c. of soda 

 required is read off, and the result expressed as the amount of n/10 

 alkali required to neutralise the acids in 100 c.c. filtered gastric 

 contents. Thus, an acidity of 40 would mean that 40 c.c. of n/10 

 sodium hydrate had been required to neutralise the acids of 100 c.c. 

 gastric contents. The result may also be expressed in terms of HC1, 

 and this is the method most useful in physiology. 1 c.cm. /i/10 alkali 

 equals 0*00365 gr. HC1 (see p. 245). If, for example, 100 c.cm. of 

 gastric juice require 50 c.cm. n/10 alkali to neutralise it, the acidity 

 in terms of HC1 will be 0-1825. In other words the percentage of HCl 

 will be 0-1825. 



