PROTEINS 239 



may be extracted with dilute salt solutions. An example of this 

 class is Edestin, which may be prepared by extracting hemp 

 seed with 5% sodium chloride solution. 



ii. Globulins of the Blood Plasma. If time permits, the vari- 

 ous blood globulins may be fractionally precipitated from blood 

 plasma. Quarter saturation brings down fibrinogen, half satura- 

 tion precipitates practically all the remaining globulins of which 

 there may be several. The filtrate from the globulins still con- 

 tains serum albumin, which may be precipitated by acidifying 

 slightly, or by saturating with ammonium sulphate. Fibrinogen 

 also may be precipitated by half saturating with NaCl, differing 

 in this respect from the other globulins which require full satura- 

 tion for precipitation. 



Fibrin. On beating freshly drawn blood with a rod, the 

 fibrinogen separates as shreds of fibrin which gather on the rod, 

 and may be washed free of corpuscles. Examine a piece of fibrin. 

 Note its elasticity. It possesses the general properties of the 

 globulins. Test its solubility in water and 10% NaCl. Filter off 

 the liquid and test it for protein by an appropriate test to ascer- 

 tain whether or not any fibrin has dissolved. In choosing your 

 test, recall the effect of sodium chloride on certain of the color 

 tests. 



Like other globulins, fibrin is soluble in dilute salt solutions, 

 but complete solution takes place only after several days' stand- 

 ing. 



On small pieces of solid fibrin suspended in water try the 

 Millon and the xanthoproteic tests. 



Myosin. This muscle globulin may be prepared from the mus- 

 cle of a freshly killed rabbit, by grinding in a mortar with 5% 

 MgS0 4 , preferably after washing out the blood vessels with 

 physiological saline. The extract contains myosin and also other 

 proteins, e.g. paramyosinogen, from which it may be separated 

 by fractional precipitation with MgS0 4 . At 50% concentration, 

 paramysinogen precipitates. 



If the concentration of the filtrate is increased to 94%, myosin 



