GASTRIC JUICE AXD CHANGES IN STOMACH. l6l 



acid ; they are not formed in the cells of the walls of the stom- 

 ach, but in the food contents. If from some pathological 

 cause the fundus glands fail to secrete hydrochloric acid or 

 secrete it in traces only, then the fermentation bacteria can 

 work unhindered on the carbohydrates in the stomach and 

 produce relatively large amounts of acid. Lactic acid is usu- 

 ally the most abundant of these fermentation products, but 

 butyric acid is occasionally formed and also acetic acid. 



The recognition of these organic acids is not difficult if they 

 are alone or mixed with only a little mineral acid. These are 

 of course the cases of practical importance ; much hydrochloric 

 acid and much lactic acid could not be found together. Among 

 the simpler reactions employed the following with iron salts 

 are the most useful : 



TEST FOR LACTIC ACID. Prepare a dilute solution of phenol by dissolv- 

 ing i gm. of the pure crystallized product in 75 cc. of water. To this add 

 5 drops of a strong solution of ferric chloride, which produces a deep blue 

 color. Five cc. of this mixture suffices for a test. Add to it a few drops 

 of the liquid containing lactic acid, and note the change from blue to 

 yellow. (Uffelmann's test) 



A weak, colorless solution of ferric chloride serves also as a test sub- 

 stance, as its color becomes much deeper by addition of a trace of lactic 

 acid. (Kelling's test.) 



This reaction is not influenced by the presence of small amounts of 

 hydrochloric acid, as can be readily shown by adding some to the liquid 

 to be tested. The color change depends on the peculiar behavior of ferric 

 salts with organic acids in general. These acids are relatively weak and 

 with ferric iron tend to form " undissociated " salts which all have a 

 deeper color than have those with the stronger acids. 



Both of these tests are much more delicate if applied to the product 

 obtained by shaking out the gastric juice or stomach contents with ether. 

 About 10 cc. of the filtered juice may be shaken with 100 cc. of ether 

 in a separatory funnel through half an hour. When the ether is drawn 

 off and evaporated slowly the lactic acid, if present, is left as a residue. 

 This residue is taken up with a few cc. of water and used for the tests. 



The Amount of Acid. It has just been shown how we 

 are able to recognize the free acids existing in the gastric 

 juice, and also, under certain conditions, that in combination 

 with the protein. An equally important problem is the deter- 

 mination of the proportions in which these fractions of the 



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