APPENDIX. 73? 



with three to four times its volume of water, sufficient dilute acetic acid 

 .should then be added to render the solution distinctly acid, and the 

 casein which is thrown down may be separated by filtration. It may 

 then be washed with alcohol and afterwards with ether, to free it from 

 fat. 



Casein may also be prepared by adding to milk an excess of crystallized 

 magnesium sulphate or sodium chloride, either of which salt causes it to 

 separate out. 



Casein gives much the same tests as alkali-albumin. It is soluble in 

 dilute acid or alkalies; it isreprecipitated on neutralization, but if potas- 

 sium phosphate be present the solution must be distinctly acid before 

 the casein is deposited. 



CLASS III. GLOBULINS. 



General Properties of Globulins. They give the general proteid 

 tests; are insoluble in water; are soluble in dilute saline solutions; 

 are soluble in acids and alkalies forming the corresponding derived- 

 albumin. 



Most of them are precipitated from their solutions by saturation 

 with solid sodium chloride, magnesium sulphate, and other neutral 

 salts. 



They are coagulated, but at different temperatures, on heating. 



(A) Globulin or Crystallin. It is obtained from the crystalline 

 lens by rubbing it up with powdered glass, extracting with water or with 

 dilute saline solution, and by passing through the extract a stream of car- 

 bon dioxide. 



It differs from other globulins, except vitellin, in not being precipi- 

 tated by saturation with sodium chloride. 



(B) Myosin. Myosin may be prepared, as was before described, 

 from dead muscle, by removing all fat, tendon, etc., and washing re- 

 peatedly in water, until the washing contains no trace of proteids, 

 mincing it, and then treating with 10 per cent solution of sodium chlo- 

 ride, or similar solution of ammonium chloride, magnesium sulphate, 

 which will dissolve a large portion into a viscid fluid, which filters with 

 difficulty. If the viscid filtrate be dropped little by little into a large 

 quantity of distilled water, a white flocculent precipitate of myosin will 

 occur. 



It is soluble in 10 per cent saline solution; it is coagulated at 60 C. 

 into coagulated proteid; it is soluble without change in very dilute 

 acids; it is precipitated by picric acid, the precipitate being redissolved 

 on boiling; it may give a blue color with ozonic ether and tincture of 

 guaiacum. The formation of a clot of myosin on dilution of the strong 

 saline solution in which it is contained, has been already commented 

 upon. 



47 



