224 PEACTICAL PHYSIOLOGY 



This constitutes the second stage of peptic digestion, audit is the pepsin 

 which produces the change. If samples of any of the other test tubes 

 be examined no proteose will be found, either because no pepsin has 

 been present (as in A and B\ or because, though present, its action has 

 been destroyed by heat (as in E), or there has been no acid present to 

 produce syntonin and help its action (as in C and F). 



There are two principal varieties of proteoses developed, namely 

 ' primary ' and ' secondary ' ; the former are precipitated by saturation 

 with sodium chloride, the latter are not (see Advanced Course). 



EXPERIMENT VI. (3) Take a sample of a digest of two days' 

 duration. Heat this to near boiling point, and add ammonium 

 sulphate crystals till no more will dissolve. Now change the reaction 

 of the fluid to alkaline and allow to cool. 1 Filter and test the filtrate 

 for Peptone. 



1. By Biuret reaction (remember to add a large excess of caustic 

 alkali, so that more than is sufficient to decompose the Am 2 S0 4 may be 

 present in the fluid) rose-pink. 



2. By nitric acid test no precipitate. This constitutes the final 

 stage in the peptic digestion of proteids. There are two varieties of 

 peptone developed, anti- and hemi-peptone, which differ from one 

 another in that the proteolytic enzyme of pancreatic juice can 

 further decompose the hemi-, but not the anti-peptone.' 2 These are 

 the products of peptic digestion only when the process is of short 

 duration. By prolonged action digestion proceeds much further and 

 yields the same crystalline products as result when a strong mineral 

 acid is allowed to act on proteid. 



The various stages can therefore be tabulated as follows : 



'(1) NATIVE PROTEID, coagulated by heat, \ Biuret test 



I = violet. 



(2) ACID ALBUMIN ATE, precipitated by neutralisation, [Alcohol 



J = coagulates. 



(3) PROTEOSE, * precipitated by HN0 3 , clear-^ Biuret test 



.2 



or pro-peptone, ing up on heating, etc. , 



Primary, precipitated by saturation with 

 NaCl, 



= pink. 

 Alcohol 



= precipitate. 



Secondary, 



(4) PEPTONE ANTI unacted on by trypsin. 2 

 HEMI acted on by trypsin. 



Besides pepsin, the gastric juice also contains the milk curdling 



1 It is only by thus saturating in the heat, both in acid and alkaline reaction, that 

 all traces of secondary albumoses are precipitated. 



2 Much doubt has recently been cast on the existence of anti-peptone (see p. 

 449). 



