128 PHYSIOLOGY OF ALIMENTATION. 



agent) broken into successively simpler compounds until the 

 amino-acids are finally reached. From the albumins, for 

 example, are derived first of all the album oses, which may well 

 be looked upon as being made up of long chains of amino- 

 acids. These now break up into shorter chains constituting 

 the peptones. In the analysis of albumin we are able to 

 recognize this stage in digestion by the appearance of certain 

 color reactions (biuret test), which it will be seen later l are 

 given by certain polypeptides which have been produced syn- 

 thetically. The peptones may therefore be looked upon as a 

 mixture of polypeptides. These polypeptides now break up 

 into still simpler chains of amino-acids passing more or less 

 directly through the stages of hexa-, penta-, tetra-, etc., pep- 

 tides until the simple mono- and diami no-acids are reached 

 The peptides giving a biuret test pass over without a break 

 into those which do not give this reaction. It is clear, there- 

 fore, that little by little the name "peptone" must disappear 

 to give way to well-defined chemical compounds. Transitiona 

 forms of all degrees of chemical complexity exist between the 

 peptones on the one hand and the simple amino-acids on the 

 other. The diagram does not show, of course, the way in 

 which any protein is hydro ly zed, but rather one or two 

 schemes according to which this may occur. 2 



1 See p. 142. 



2 ABDERHALDEN: Lehrbuch d. physiol. Chemie, Berlin, 1906, p. 206 



