276 PHYSIOLOGICAL CHEMISTRY 



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 tes.t 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 

 is thrown down. It may be prepared and its reactions studied 

 if time permits. 



The solid meat residue left after extracting the myosin is 

 known as ' ' muscle stroma. ' ' It contains some coagulated myosin, 

 and probably members of other groups. Test it by the xantho- 

 proteic reaction and Millon 's test. 



N euro globulins. Two and perhaps three globulins occur in 

 the brain. They may be prepared by extraction with salt solu- 

 tions and occur chiefly in the grey matter and the axis cylinders. 



Prolamines. The best known member of this group of alco- 

 hol soluble proteins is the gliadin of wheat. 



23. Two students may work together. To about 50 gms. of 



