THE PROTEINS. 23 



GLOBULINS. 



As a class the globulins are characterized by their insolu- 

 bility in water and solubility in weak salt solutions (5-10 per 

 cent). A suitable solution of a typical globulin (edestin) is 

 easily prepared by extracting finely ground hemp-seed for 

 an hour with a 10 per cent solution of NaCl, and finally 

 filtering the mixture through paper. The edestin may be 

 obtained in crystalline form if the extraction of the seed is 

 made with a 5 per cent solution of NaCl at 55 C. and the 

 extract filtered through a hot-water funnel. Upon cooling 

 the protein separates out of the solution in well-formed and 

 characteristic crystals, hexagonal in shape. 



(a) Try two protein color reactions and three precipita- 

 tion reactions. Test the coagulability of the solution. 



(6) Pour some of the solution, drop by drop, into a beaker 

 of water. A precipitation of the globulin occurs owing to 

 the decrease in the percentage of salt in the solution by dilu- 

 tion. A similar precipitation may also be accomplished by 

 removing the salts by dialysis. 



(c) Start dialysis experiment. A very simple form of 

 dialyzer can be arranged as follows: 



Select a beaker and a funnel whose stem has been removed 

 at the neck and whose diameter is somewhat greater than 

 that of the beaker. Allow the funnel to hang in the beaker 

 resting upon its rim. Cut and fold some well-moistened 

 parchment paper in the manner of a filter and place it in the 

 funnel. Fill the beaker nearly to the top with water and 

 pour into the parchment filter enough of the solution to be 

 dialyzed so that it about half fills it. The levels of the inner 

 and outer fluids should correspond. 



In 24 hours note carefully any changes which may have 

 occurred. What has caused them? 



(d) Saturate 10 c.c. of the globulin solution with MgS0 4 . 



