APP. IV.] COLOUR REACTIONS OF THE GASTRIC JUICE. 495 



V. 



NOTES AND ADDITIONS ON THE NATURE OF THE ACIDS 

 OF THE GASTRIC JUICE AND GASTRIC CONTENTS 1 . 



1. ON THE COLOUR REACTIONS WHICH MAY BE EMPLOYED IN THE 

 INVESTIGATION OF THE AdDS OF THE GASTRIC JUICE AND 

 GASTRIC CONTENTS. 



(Supplementary to pages 92 95 and 179.) 



The reader who has perused the account given of the various 

 colouring methods which may be employed either as indicators of the 

 total acidity of the gastric juice, to discover the presence of free 

 hydrochloric acid, or of free acids, mineral and organic, will be con- 

 scious of the want of more definite information as to the special 

 advantages which certain reagents possess over others. This want is 

 supplied by the results of the observations of Martius and Liittke, 

 and to certain of these we shall draw the attention of the reader. 



Behaviour of The compounds of albumin with hydrochloric acid 

 of th^aibu- behave towards litmus as free acids ; it follows there- 

 minous sub- f re tnat even ^ n tne absence of free HC1, litmus may 

 stances with be reddened by the contents of the stomach. It is 

 HCI towards indeed very rare that the contents of the stomach 

 possess a neutral or alkaline reaction. Litmus is, un- 

 like phenolphthalein, not affected by solutions of acid phosphates. 

 Some hydrochlorates of organic bases give an alkaline reaction with 

 litmus, whilst with phenolphthalein they exhibit an acid reaction 3 . 



Behaviour of Phenolphthalein is a body which has of recent years 



the compounds come into very general use as an indicator in the 



I alb - titration of acids and alkalies, and which possesses 



stances with s P ec i a l advantages when it is desired to determine the 



HCI towards total acidity of the gastric juice. It is therefore essen- 



'phenoiphtha- tial to know in what respect its action differs from that 



Wto - 1 of litmus. 



1 These notes and additions are mainly based on the researches and writings of 

 Martius and Liittke. See Die Magensdure des Menschen. Kritisch und experimentell 

 bearbeitet von Dr F. Martius, A. 0. Professor u. Direktor der med. Poliklinik in 

 Rostock und J. Liittke, Chemiker in Rostock. Stuttgart, Verlag von Ferdinand Enke, 

 1892. 



2 Martius and Liittke, op. cit. 39. 



3 Salkowsky und Kumagawa, ' Ueber den Begiiff der freien und gebundenen 

 Salzsaure im Mageninhalt,' Virchow's Archiv, Vol. cxxn. (1890), pp. 235252. 



