CHAPTEE I 

 Reactions of Albuminous Substances 



ALL albuminous substances are built up on the same chemical principle, 

 and have therefore a number of reactions in common. Not one of 

 these reactions is characteristic of albumins, if taken by itself ; but if 

 any substance gives several or all of the reactions described below, 

 then we are permitted to class it amongst the albumins. 1 



The author has endeavoured to trace each test back to its 

 originator. 



I. COLOUR TESTS C 



No colour reactions, with the exception of the biuret-test, are 

 characteristic of albuminous substances as such, for they all depend on 

 the presence of certain n on -albuminous compounds, or groupings of 

 atoms occurring normally in albumins in such a form as to allow of 

 interaction with the reagents. All tests, excepting the biuret-test, prove 

 simply the presence or absence of certain radicals, thereby allowing 

 us to differentiate between various kinds of albumins. 



1. The Biuret-Readion of Rose and Wiedemann 



Add to a watery solution of an albumin a sufficiently large amount 

 of soda or potash solution, and then add a few drops of a dilute 

 solution of copper sulphate, when with the native albumins a blue or 

 violet colour, and with dissociation -products such as albumoses or 

 peptones, and also with certain vitellines and histones, a pure red 

 colour is obtained. In performing the test an excess of copper 

 sulphate must be avoided, as it is apt to obscure the reaction because 

 of its own blue colour ; and the solution should not be heated, because 

 many peptones are decomposed by heat. 



1 The older literature up to 1893 is fully dealt with in J. W. Pickering's paper, 

 Journal of Physiology, 14. 347 (1893), while the more recent literature is given more 

 fully than here in Mann's Physiological Histology (Clarendon Press, 1902). 



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