EXAMINATION OF BLOOD. 59 



in water, serum globulin, kept in solution by the salts and 

 the alkali of the serum. 



I. Precipitation of the Proteids by Salts. 



Grind in a mortar 20 cc. of blood-serum with an excess of 

 ammonium sulphate (about 15 g.) for a considerable time, or 

 repeat the process, so that the fluid is completely saturated 

 with ammonium sulphate: by this means both the proteids 

 are precipitated. Filter through a dry filter. The filtrate 

 is perfectly free from albumin; when heated to boiling and 

 acidified with acetic acid it remains clear. 



II. Separation of Serum Albumin and Serum Globulin. 



Fifty to one hundred cubic centimeters of blood-serum (or 

 serous transudate) are treated with an equal volume of a 

 saturated solution of ammonium sulphate, filtered and washed 

 with a half-saturated solution of the salt. In the filtrate the 

 serum albumin will be found (shown by heating to boiling) ; 

 the precipitate is serum globulin. It dissolves when brought 

 into water owing to the ammonium sulphate adhering to it ; 

 this solution coagulates on heating. For the preparation of 

 pure serum albumin or serum globulin this method is not suit- 

 able, since the adhering salts can only be separated by dialysis, 

 and the removal of ammonium sulphate by this means is only 

 accomplished with great difficulty. Therefore it is necessary 

 to saturate the blood with pulverized magnesium sulphate 

 and wash the precipitate with a saturated solution of the 

 same salt. 



Both methods are generally regarded as being of equal 

 value. They are, however, not quite equivalent: the quan- 

 tity of precipitate obtained by the use of ammonium sulphate 

 is larger than that with magnesium sulphate. 



The precipitate obtained by means of magnesium sul- 

 phate is also soluble in water on account of the magnesium 



