Ill THE RED CORPUSCLES 97 



again. The addition of a little water, or dilute acids 

 or saline solutions, will at once cause the rolls to 

 break up. 



It is from this running together of the corpuscles into 

 patches of network that the change noted above in the 

 appearances of the layer of blood, viewed with a lens, 

 arises. So long as the corpuscles are separate, the sandy 

 appearance lasts ; but when they run together, the layer 

 appears patchy or spotted. 



The red corpuscles, rarely, if ever, all run together into 

 rolls, some always remaining free in the meshes of the 

 net. In contact with air, or if subjected to pressure, 

 many of the red corpuscles become covered with little 

 knobs, so as to look like minute mulberries — an appear- 

 ance which is due to the concentrating by evaporation of 

 the fluid in which they are floating (Fig. 31, H, H.). 



The red corpuscles ai'e very soft, flexible, and ela.stic 

 bodies, so that they readily squeeze through apertures and 

 passages narrower than their own diameters, and imme- 

 diately resume their proper shapes (Fig. 25, G, H.). 

 Examined under even a high power the red corpuscle 

 presents no very obvious structiu-e ; when however blood 

 is frozen and thawed one or more times, or when it is 

 treated in certain other ways, as, for instance, by the 

 addition of water, the colouring matter which gave each 

 corpuscle its yellow or yellowish-red tinge is dissolved out 

 and passes into the surrounding fluid, and all that is left 

 of the corpuscle is a colourless framework appearing often 

 under the microscope as a pale, hardly visible, ring. 

 Each corpuscle in fact consists of a sort of spongy colour- 

 less framework, the stroma, composed of the kind of 

 material known as protein and of a peculiar colouring 

 matter, which, in the natural condition, is intimately 

 connected with this framework, but may by appropriate 

 means be removed from it. This colouring matter, which 

 is of a highly complex nature, is called hsemoglobin, 

 and may by proper chemical treatment be resolved into a 



