THE BLOOD. 25 



(a.) Take 10 cc. of blood-serum ; add 200 cc. of ice-cold 

 water, and pass a stream of carbon dioxide through it for 

 some time = a white precipitate of serum-globulin. This 

 method does not precipitate it entirely (Schmidt's method). 

 No precipitate is obtained unless the serum be diluted. 



(b.) Dilute 10 cc. of blood-serum with 150 cc. of water; 

 add 5 drops of a 20 per cent, dilution of acetic acid = a 

 white precipitate of serum-globulin, or as it was called, 

 " serum-casein " (Panum's method). All the serum-globulin 

 is not precipitated. 



(c.) To 5 cc. of fresh blood-serum in a test-tube, add 

 crystals of magnesium sulphate in large excess, and shake 

 briskly for some time. The excess of crystals falls to the 

 bottom, and on their surface is precipitated a dense white 

 flocculent mass of serum-globulin (Hammarsten's method). 

 Allow the excess of the salt and the precipitate to settle. 

 Decant the bulk of the supernatant fluid, and filter the 

 remainder. Wash the precipitate on the filter with a 

 saturated solution of magnesic sulphate ; add a little dis- 

 tilled water to the precipitate. It is dissolved i.e., it is a 

 globulin, and is insoluble in excess of a neutral salt, but is 

 dissolved by a weak solution of the same. The solution 

 does not coagulate spontaneously. 



(d.) The solution obtained in (c.) gives all the reactions 

 for proteids with the special reactions of a globulin. 



(e.) Allow a few drops of blood-serum to fall into a large 

 quantity of water, and observe the milky precipitate of a 

 globulin = serum-globulin. This is best observed by 

 placing a dead black surface behind the vessel of water. 

 We can then trace the "milky way " of the falling drops of 

 serum as they mix with the water. 



(B.) Serum-Albumin. From (A.), (.),-(&.), (c.), filter off the 

 precipitate, and test the filtrate for the usual proteid reactions, so 

 that the filtrate still contains a proteid which is serum-albumin 

 (Lesson I., 5, 2). 



14. Precipitation by other Salts. 



(a.) Precipitate the serum-globulin of blood-serum with 

 magnesic sulphate. Filter, and to the filtrate add sodic 



