PROTEINS 243 



in excess of the acid. Allow to settle, decant most of the liquid, 

 and if the precipitate is sufficiently heavy, filter and use small 

 portions of the residue for the following tests. If the precipitate 

 is very slight, use portions of the saliva containing the pre- 

 cipitated mucin from which most of the clear supernatant liquid 

 has been poured off. 



ii. On a portion of the mucin suspended in water try the 

 biuret and the xanthoproteic tests. The tests should be positive. 



iii. Hydrolyze a portion of the mucin by boiling with dilute 

 HC1, and, with portions of the liquid, test for sulphate, and for 

 carbohydrate. The tests should be positive. 



2. Hemoglobins. The hemoglobins are compounds consist- 

 ing of a protein combined with hemochromogen or some similar 

 substance. In connection with the study of hemoglobin, some 

 other constituents of blood will be considered. Recall the inor- 

 ganic materials present in blood as determined in an earlier 

 chapter. What proteins have been observed in the blood earlier 

 in this chapter ? In blood are also found fat, sugar, extractives, 

 protein decomposition products and various other substances. 



i. Spectroscopic behavior of hemoglobin. Study the spectro- 

 scopic behavior of hemoglobin and its derivatives as follows, two 

 students working together. 



(a) Oxygenation of Hemoglobin. The color of oxy hemoglobin 

 is a much lighter and more brilliant red than that of hemoglobin. 

 Dilute defibrinated blood with 5 volumes of water. The blood 

 is ' ' laked, ' ' that is, the hemoglobin leaves the corpuscles and goes 

 into solution in the water. The liquid, which was opaque, be- 

 comes clear. Laking may be brought about in various other 

 ways, as by the addition of a small amount of ether, toluol, etc. 

 Shake up the laked blood with air, closing the tube with the 

 thumb. The color becomes bright red, as the hemoglobin is 

 changed into the brighter colored oxyhemoglobin. 



Prepare three test tubes of this diluted blood. To two of 

 them add Stokes' fluid. (This is a mild reducing agent, which 

 contains 2% Fe S0 4 , 3% tartaric acid, and ammonia in amount 

 sufficient to redissolve the precipitate which forms on first adding 



