28 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



nucleic acids vary according to their content of carbohydrate 

 nucleus, purine and pyrimidine bases. 



Impure nucleins may be prepared for study by thorough 

 digestion of a nucleoprotein-containing tissue with pepsin- 

 hydrochloric acid and extraction of the residue with NH 4 OH. 

 The nuclein is then precipitated from the solution with 

 dilute HC1. 



(a) Try the solubility of the substance in water, dilute 

 alkali and alcohol. 



(6) Try three color protein tests. 



(c) Boil some with 10 per cent H 2 S0 4 for 5 minutes, 

 cool, add an excess of NH 4 OH, and finally a few drops of 

 AgN0 3 solution. Of what is the precipitate indicative? 



(d) Treat a little of the substance in a crucible with some 

 fusion mixture. Test the fused mass for phosphorus. 



DERIVED PROTEINS. 



These substances may be subdivided into primary and 

 secondary derivatives according as the hydrolytic change is 

 slight or more deep seated. 



1. PRIMARY PROTEIN DERIVATIVES. 

 (A) Metaproteins. Products of the action of acids and 

 alkalies whereby the protein molecule is so far altered as to 

 form products soluble in very weak acids and alkalies but 

 insoluble in neutral fluids. 



ACID AND ALKALI ALBUMINATES. 



The albuminates are modified proteins derived from 

 either albumins or globulins by the action of acids and alkalies 

 with the aid of heat. They are non-coagulable by heat 

 except when held in suspension in the solutions from which 

 they have been precipitated by neutralization respectively 



