4 ! 4 THE BLOOD. [CH. xxvi. 



They may be separated by dialysis or the use of neutral salts.* 

 The readiest way to separate them is to add to the serum an 

 equal volume of saturated solution of ammonium sulphate. This 

 is equivalent to semi-saturation, and it precipitates the globulin. 

 If magnesium sulphate is used as a precipitant of the globulin 

 it must be added in the form of crystals, and the mixture well 

 shaken to ensure complete saturation. 



Serum globulin was formerly called fibrinoplastin, because it 

 was belieA r ed to take some share in fibrin formation. It is also 

 called paraglobulin. It may be imperfectly precipitated by 

 diluting serum with twenty times its volume of water and then 

 adding a trace of acetic acid, or passing a stream of carbonic acid 

 gas through the diluted serum. 



Fibrin-ferment. Schmidt's method of preparing it is to take 

 serum and add excess of alcohol. This precipitates all the 

 proteids, fibrin-ferment included. After some weeks the alcohol 

 is poured off; the serum globulin and serum albumin have been 

 by this means rendered insoluble in water ; an aqueous extract is, 

 however, found to contain fibrin-ferment, which is not so easily 

 coagulated by alcohol as the other proteids are. 



B. Extractives. These are non-nitrogenous and nitrogenous. 

 The non-nitrogenous are fats, soaps, cholesterin, and sugar,, the 

 nitrogenous are urea (0*02 to 0^04 per cent.) and still smaller 

 quantities of uric acid, creatine, creatinine, xanthine, and hypo- 

 xanthine. 



C. Salts. The most abundant salt is sodium chloride ; it con- 

 stitutes between 60 and 90 per cent, of the total mineral 'matter. 

 Potassium chloride is present in much smaller amount. It consti- 

 tutes about 4 per cent, of the total ash. The other salts are 

 phosphates and sulphates. 



Schmidt gives the following table : 

 1000 parts of plasma yield 



Mineral matter 8*550 



Chlorine 3 '640 



S0 8 0-115 



P 2 5 0-191 



Potassium ....... o - 323 



Sodium 3 -341 



Calcium phosphate . . . . . 0-311 



Magnesium phosphate 0*222 



The Blood-Corpuscles. 



There are two principal forms of corpuscles, the red and the 

 white, or, as they are now frequently named, the coloured and the 

 colourless. In the moist state the red corpuscles form about 40 per 



* The globulin of the serum precipitated by 'salting out' really consists 

 of two proteids, one of which is precipitated by dialysis, and the other is not. 



