318 THE BLOOD 



solution, so that the corpuscle is not subjected to osmotic strain, 

 appears yellow and somewhat opaque. If now, the capsules of the 

 corpuscles are damaged so that the Hb is set free and goes into 

 solution in the aqueous saline solution, the liquid will become 

 translucent and a deep red in colour. This is known as haemolysis, 

 and haemolysed blood, because it is similar in colour to crimson- 

 lac-resin (a gum extruded from tropical trees after puncture by 

 the lac insect), is said to be laked. 



Blood may be laked by various methods : 



1. Mechanical, grinding corpuscles with sand or powdered glass 

 and taking up with salt solution. 



2. Physical, freezing and thawing, heat, condenser discharges, 

 or similar methods. 



3. Endosmosis, dropping blood into water or into a hypo-tonic 

 solution. 



4. Exosmosis (see crenation), dropping blood into a hypertonic 

 solution. 



5. Action on Lipoid constituents of capsule. 



i. Anaesthetics are lipoid solvents. 



ii. Bile salts and pigments affect permeability of lipoid 

 membranes. 



iii. Glucosides, e.g. saponin, are adsorbed by the membrane 

 (Willard Gibbs' Law), because they lower surface 

 tension. They then insert themselves into the texture 

 of the membrane and increase its permeability (see 

 p. 138). 



6. Biological Agents. 



i. Toxins of certain bacteria produce haemolysis, e.g. 



tetanolysin of B. Tetani ; megatheris lysin of B. 



Megatherium ; toxic lysins of staphylococcus and 



B. pyocyaneus. 

 ii. Cobra and rattlesnake venom cause laking both in vivo 



and in vitro. 

 iii. The serum of one animal is often haemolytic for the 



blood of a different species. 

 iv. Certain phyto-albumins, e.g. abrin, ricin, and robin, 



produce haemolysis. 



7. Chemical Agents. 



Haemolysis may be caused by the ingestion or injection of 

 certain drugs, e.g. chlorates, nitrites, nitrobenzene, aniline deriva- 

 tives {e.g. acetanilide and phenacetin), quinine. These, generally, 

 partially convert the haemoglobin into methaemoglobin [q.v.). 



The laking of blood thus depends on altering the permeability 

 of the capsule of the erythrocyte. Normally this membrane is 



