476 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



(4) Laking of Blood. Haemolysis. 



Blood, or defibrinated blood, is opaque even in very thin layers 

 but becomes transparent when the haemoglobin, which is normally 

 contained in the red blood corpuscles, is discharged from them. The 

 blood is said to be laked or haemolysed. 



Blood may be laked in several ways : 



(a) By osmosis, i.e. by diluting it with 2 or 3 volumes of water, or 

 by adding blood to excess of water. A solution is obtained which is 

 transparent and has a bright red colour. In the process of osmosis water 

 passes into the corpuscles, bursts them and liberates the haemoglobin. 

 This does not occur when blood is mixed with 0-9 per cent, sodium 

 chloride solution, since the contents of the corpuscles and the saline 

 -solution have the same osmotic pressure or are isotonic. 



More concentrated solutions of salt produce crenation of the cor- 

 puscles since water is withdrawn from them. Such solutions are 

 hypertonic ; more dilute solutions are hypotonic. 



(b) By the action of weak alkali. Blood is mixed with -9 per cent. 

 sodium chloride solution and a few drops of alkali are added. The 

 blood becomes transparent. 



(<:) By the action of chloroform or ether. Blood diluted with -9 per 

 cent, salt solution becomes transparent if a few drops of ether of chloro- 

 form are added and mixed with it 



(cf) By alternate freezing and thawing. The blood on subsequent 

 dilution with "9 per cent sodium chloride will be transparent. 



(e) By the action of urea. Blood mixed with an isotonic solution 

 of urea becomes transparent. 



(/) By glucosides such as saponin. 



(g) By bacterial toxins, snake venoms and by the blood serum 

 of another animal. 



(5) The Catalytic Action. 



Blood contains a very active catalytic enzyme, or catalase, which 

 is sometimes termed haemase. An evolution of oxygen occurs on add- 

 ing a little hydrogen peroxide to defibrinated blood. 



(6) The Peroxidase Action. 



Blood, owing to the presence of haemoglobin, gives very marked 

 peroxidase reactions (p. 411). 



(a) With Guaiacum. 



One drop of blood is diluted considerably with water (about 10 c.c.), 

 one-half of its volume of hydrogen peroxide (20 vols. per cent.) is 

 tnixed with the solution and upon the surface is floated some fresh 

 tincture of guaiacum or better a I per cent, alcoholic solution of guaia- 

 conic acid. A blue colour gradually develops above the resinous ring 



