12 



BLOOD 



are circular, biconcave, non -nucleated discs of a yellowish 

 colour. They consist of a stroma containing hsemoglobin. 

 This is probably surrounded by an envelope of lecithin 

 and cholesterin. The corpuscles are flexible, and by alter- 

 ing their shape can squeeze through apertures smaller 

 than themselves. They are pervious only to substances 



Fig. 1. — The spectra of haemoglobin and its derivatives. 1-4, Oxy- 

 hsemoglobin in increasing concentration ; 5, reduced haemoglobin ; 

 6, carboxyhsemoglobin. (After Preyer and Gamgee, from Starling's 

 Princi'plcs of Physiology.) 



such as alcohol, chloroform, urea, which are soluble in 

 lecithin and cholesterin. They are impervious to inorganic 

 salts. In standing blood the corpuscles tend to clump 

 together into roulettes. Concentration of the saline con- 

 stituents of the plasma causes a shrinking of the corpuscle, 

 while dilation causes the reverse, viz. swelhng up and burst- 

 ing with hberation of the haemoglobin. The latter process, 

 known as " haemolysis," can also be brought about by treat- 



