116 THE BLOOD 



The chief methods of obtaining plasma free from corpuscles are: i. By cold. The 

 temperature should be about o C. and may be two or three degrees higher, but not 

 lower. 2. The addition of neutral salts, in certain proportion, either as solids or in 

 solution, e.g., of sodium sulphate, if solid i part to 12 parts of blood; if a saturated solu- 

 tion i part to 6 parts of blood. Or magnesium sulphate, saturated solution i part to 

 4 of blood. 3. By mixing frog's blood with an equal part of a 5 per cent solution of 

 cane sugar, and getting rid of the corpuscles by nitration. 4. By the injection of com- 

 mercial peptone into the veins of certain mammals previous to bleeding them to death, 

 allowing the corpuscles to subside or by subjecting the blood to the action of a centrif- 

 ugal machine by the rapid rotation of which the whole of the solids are driven to the 

 outer end of the tubes in which the blood is placed. 



PERCENTAGE COMPOSITION OF PLASMA. 



Water 90.29 



Solids 



1. Proteids 

 Fibrinogen } 



Paraglobulin I 8.289 



Serum albumin ) 



2. Extractives 566 



3. Inorganic salts 8 ;o 



9.71 



Water. The water of the plasma varies in amount according to the 

 amount of food, drink, and exercise, or other circumstances. It amounts 

 to about 90 per cent. 



Proteids. Fibrinogen is the substance in plasma which is converted into 

 fibrin on coagulation. It belongs to the class of proteids called globulins. 

 It is precipitated from plasma with serum globulin by saturation with MgSO 4 

 and NaCl. It is soluble in dilute salt solutions but is not soluble in water. 

 It can be distinguished from serum globulin by a number of special reactions; 

 i. Its coagulation temperature is lower, 55 to 56 C. 2. It is completely 

 precipitated by saturation with NaCl as well as with MgSO 4 . 3. It gives 

 rise to an insoluble proteid, fibrin. It may be, however, that fibrinogen is 

 not a simple proteid, but a mixture or loose chemical combination of two 

 or more proteids. Fibrinogen is present in plasma to the extent of 0.2 to 

 0.5 per cent. 



Serum globulin or paraglobulin is similar to fibrinogen in its reactions. 

 It is completely precipitated by MgSO 4 ; incompletely by NaCl, and co- 

 agulates at a temperature of 75 C. It is likewise soluble in dilute salt solu- 

 tions but insoluble in water. It is present in plasma in from 3.5 to 4 per cent. 



Serum albumin is the proteid which predominates in human plasma. 

 It is readily obtained in crystalline form; is soluble in MgSO 4 and NaCl 

 solutions, but insoluble in saturated ammonium sulphate solutions; and 

 coagulates in neutral or acid solutions at from 73 to 75 C. 



Extractives. The extractives are the nitrogen-containing substances 

 such as urea, uric acid, creatin, creaiinin, etc.; glycogen, dextrose, choles- 



