VISCOSITY 243 



The stroma (and capsule) are colloidal in character. The 

 enmeshed fluid is also colloidal and, therefore, the corpuscle as 

 a whole will act as a colloid. Acids increase the power of colloids 

 to imbibe water and, therefore, one would expect that CO 2 would 

 cause an increased imbibition of water by the corpuscles and, 

 consequently, increase the viscosity of blood, due (a) principally 

 to the absorption of water from the plasma rendering it more 

 viscous and (6) the swelling of the corpuscle itself. The experi- 

 mental proof of this has not been very satisfactory, but some 

 workers have observed increased viscosity in venous blood, 

 especially in cases where the unsaturation of haemoglobin is low 

 (pneumonia, gas poisoning). 



Viscosimetric measurements afford a means of determining the 

 volume of blood corpuscles. Viscosity depends principally on 

 the total volume of corpuscles per unit volume of fluid. Having 

 determined (i) the viscosity of whole blood =pc, and (ii) that of 

 the plasma p, the total corpuscular volume K may be derived 

 from the formula 



1 -K=". 



pc 



If the total number of corpuscles per unit volume be N, then 

 the average volume of each will be K/N. 



The results obtained from such an indirect method are fairly 

 regular but cannot be considered as absolutely accurate, as 

 viscosity does not depend, in principle, on either the number or 

 the volume of corpuscles, but on the effective surface, i.e. on the 

 area liable to friction (see relation between viscosity and blood- 

 pressure). 



The sponge-work, which is a colloidal complex of protein, 

 lecithin, kephalin, cholesterol, etc., with adsorbed electrolytes, 

 encloses water and electrolytes in solution and the pigment 

 haemoglobin. This pigment is an electropositive protein con- 

 taining 0-399 per cent. iron. It is not in true solution in the 

 corpuscles. The corpuscle contains 32 per cent. Hb in 63 per cent, 

 water, while the solubility in water is 18 per cent. It may be 

 set free by rupturing the corpuscle. 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. 



