20 TEXT-BOOK OF PHYSIOLOGY 



The Color Reactions of Proteins. When proteins are present in 



solution, they may be detected by the following color reactions viz. , 



r. Xanthoproteic. The solution is boiled with nitric acid for several 



minutes, when the protein assumes a light yellow color. After 



the solution has cooled, the addition of ammonia changes the color 



to an orange or amber-red, due to the presence of phenylalanin and 



ty rosin. 



2. The rose-red reaction. The solution is boiled with acid nitrate of 



mercury (Millon's reagent) for a few minutes, when the coagulated 

 protein turns a purple-red color. This color is attributed to the 

 presence of tyrosin. 



3. The blue- violet reaction. To the solution is added an excess of sodium 



hydroxide, at least an equal volume, and then drop by drop, a very 

 dilute solution of copper sulphate. A blue-violet color is produced, 

 which deepens somewhat on heating, but no further change ensues. 

 This is also known as Piotrowski's test: As this same color is de- 

 veloped with the substance biuret, it is also known as the biuret 

 reaction. Biuret is formed by heating urea to i8oC and driving off 

 ammonia. 



Precipitation Tests. Proteins in solution may be precipitated by 

 nitric acid, acetic acid and potassium ferrocyanid, picric acid, copper 

 sulphate, tannin, alcohol, etc. As stated in a foregoing paragraph, certain 

 of the proteins, e.g., fibrinogen, caseinogen and myosinogen, will undergo, 

 by the action of an animal ferment a change of state by virtue of which 

 they become solid. To this process the term ferment coagulation is applied. 

 The solidification of proteins by the action of heat is designated heat 

 coagulation. 



INORGANIC CONSTITUENTS 



The inorganic compounds and mineral constituents obtained from the 

 solids and fluids of the body are very numerous, and, in some instances, 

 quite abundant. Though many of the compounds thus obtained are 

 undoubtedly derivatives of the tissues and necessary to their physical and 

 physiologic activity, others, in all probability, are decomposition products, 

 or transitory constituents introduced with the food. Of the inorganic 

 compounds, the following are the most important: 



WATER. 



Water is the most important of the inorganic constituents, as it is in- 

 dispensable to life. It is present in all the tissues and fluids without excep- 

 tion, varying from 99 per cent, in the saliva to 80 per cent, in the blood, 75 

 per cent, in the muscles to 2 per cent, in the enamel of the teeth. The total 

 quantity contained in a body weighing 75 kilograms (165 pounds) is 52.5 

 kilograms (115 pounds). Much of the water exists in a free condition, and 

 forms the chief part of the fluids, giving to them their characteristic degree of 

 fluidity. Possessing the capability of holding in solution a large number of 

 inorganic as well as some organic compounds, and being at the same time 

 diffusible, it renders an interchange of materials between all portions of the 

 body possible. It aids in the absorption of new material into the blood and 

 tissues, and at the same time it transfers waste products from the tissues to 



