BLOOD. 



Blood may be considered as composed of a fluid plasma 

 in which are suspended the form elements, i.e., the red 

 corpuscles, the leucocytes, and the platelets. When the 

 plasma coagulates, there separates from it the insoluble 

 fibrin or the clot, and the fluid which remains or is pressed 

 out by the contraction of the clot, is designated as the serum. 

 The reaction of the blood is alkaline to litmus, the alkalinity 

 being equivalent to about 0.25 per cent Na 2 C0 3 . As was the 

 case with the other body fluids, it is also acid to phenol- 

 phthalein, since it contains sodium bicarbonate and dihy- 

 drogen phosphate. 



The specific gravity of the blood varies within rather 

 small limits, 1.055-1.066, and the molecular concentration, 

 as indicated by the depression of the freezing point, is under 

 normal conditions almost constant. Approximately 60 per 

 cent by weight of the blood is composed of corpuscles and 

 the remaining 40 per cent of plasma. 



General Reactions. 



Test the reaction with litmus paper previously moistened 

 with a concentrated solution of NaCl. To what is this reac- 

 tion due? Specific gravity see Hammarsten, p. 223, Ham- 

 merschlag's method. 



(a) Examine a drop under the microscope. 



(6) To 5 c.c. of blood add 10 c.c. of water. Notice 

 changes in the solution and examine a drop under the micro- 

 scope. What is laky blood? 



(c) To 5 c.c. of blood add 10 c.c. of an 0.8 per cent NaCl 

 solution. Examine a drop of this also. What is meant by 



a solution isotonic with blood? 



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