3 HUMAN PHYSIOLOGY 



6. Proteids are precipitated by some weak organic acids 

 or their salts in a solution of acetic acid : hydroferrocyanic 

 acid, potassium ferrocyanide and acetic acid, tannic acid, 

 picric acid, trichloracetic acid. In this case also compounds 

 insoluble in water are formed, in which the proteids seem to 

 take the part of a base. 



7. Proteids are also precipitated by phosphotungstic and 

 phosphomolybdic acids and potassio-mercuric iodide in the 

 presence of free hydrochloric acid. 



B. Color reactions of proteids. 



1. Xanthoproteic reaction. Proteids boiled with strong 

 nitric acid turn yellow, which is colored orange by ammonia. 



2. Mil Ion' s reaction. Proteids boiled with mercuric 

 nitrate solution containing excess of nitric acid are colored 

 brick-red. This coloration depends upon the oxyphenyl 

 nucleus of the proteids (as in case of tyro sin). 



3. Biuret reaction. If to a solution of proteid, sodium 

 hydrate and dilute copper sulphate be added, a violet or 

 rose-red color results. Biuret, a derivative of urea, also 

 gives this reaction. 



4. Adamkiewics' reaction. To a solution of proteids in 

 acetic acid, add excess of concentrated sulphuric acid. A 

 reddish-violet color appears. 



(e) Physiological Importance of Proteids. 



The albuminous bodies are the most important constitu- 

 ents of our body, for all tissues and organs are composed 

 of them. Hence they are also called the proteids (from 

 TTpoorevGo). They form the chemical and physical basis of 

 the living substance and are present in the body partly in a 

 solution, e.g. the tissue fluids and cell saps; partly in a solid 

 form (more or less swollen), forming the cells and tissues. 



The proteids (including the albuminoids) form about one 

 sixth of the body weight. About one half of all the proteids 

 of the body are contained in the muscles, which are composed 

 of about 20f proteids. The liver, spleen, and blood also 

 contain the same percentage of proteid. The nerves, brain, 



