LESSON IX 

 THE BLOOD AND RESPIRATION 



[Blood Plasma. 



1. The coagulation of the blood has been prevented in specimen A by the 

 addition of neutral salt (an equal volume of saturated sodium- sulphate 

 solution, or a quarter of its volume of saturated magnesium-sulphate solu- 

 tion). The corpuscles have settled, and the supernatant salted plasma has 

 been siphoned off. 



2. The coagulation of the blood in specimen B has been prevented by the 

 addition of an equal volume of ai 0'4-per-cent. solution of potassium oxalate 

 in normal saline solution. 



3. Put a small quantity of A into three test-tubes and dilute each with 

 about ten times its volume of liquid : 



A 1. With distilled water. 



A 2. With solution of fibrin ferment containing a little calcium chloride. 1 



A 3. With the same. 



4. Put A 1 and A 2 into the water-bath at 40 C. ; leave A 3 at the tem- 

 perature of the air. A 1 coagulates slowly or not at all ; A 2 coagulates 

 rapidly : A 3 coagulates less rapidly than A 2. 



5. Add to some of B a few drops of dilute (2 per cent.) calcium-chloride 

 solution : it coagulates, and more quickly, if the temperature is 40 C. 



Blood Serum. 



Blood serum is the fluid residue of the blood after the separation of the 

 clot ; it is blood plasma minus the fibrin which it yields. The general ap- 

 pearance of fibrin obtained by whipping fresh blood will already be familiar 

 to the student, as he has used it in experiments 011 digestion. 



Serum has a yellowish tinge due to serum lutein, but as generally obtained 

 it is often contaminated with a small amount of oxyhaemoglobin, and so looks 

 reddish. It contains proteins (giving the general tests already studied in 

 Lesson IV.), extractives, and salts in solution. The proteins are serum 

 albumin and serum globulin. The fibrin ferment is also a protein-like sub- 

 stance. It is present in only small quantities, and in the following experi- 

 ments is precipitated with serum globulin. 



Separation of the serum proteins, (a) Dilute serum with fifteen times 

 its volume of water. It becomes cloudy owing to the partial precipitation of 



1 An easy way of preparing an impure but efficient solution of fibrin ferment 

 is to take 5 c.c. of blood serum and dilute it with a litre of distilled water. A 

 partial precipitation of globulin takes place, and carries down the ferment with it. 

 After a few hours pour off the supernatant fluid and dissolve the precipitate in 

 half a litre of tap-water to which a few drops of 2-per-cent. solution of calcium 

 chloride have been added. The solution can be then given round to the class as 

 fibrin ferment. 



