BLOOD. 113 



biconvex. Each cell possesses an oval nucleus, which causes a 

 thickening in the centre. They are much larger than in mam- 

 mals. In Rana temporaria they are 22 p long, 15 p broad; in 

 Salamandra maculosa, 37 f* long, 23^ broad; in Proteus san- 

 guineus, 58 {i long and 34^ broad. 



The red blood-cell in man consists of two constituents, a 

 protoplasmic part (stroma) and the coloring matter distributed 

 on this i. e., the hcemoglobin. Anilin-stains, such as eosin, 

 orange G, etc., are taken up readily by haemoglobin-containing 

 cells. 



Under the influence of reagents, red blood-corpuscles change 

 their form very quickly. In water or dilute acids they swell 

 up arid lose their haemoglobin. They are then colorless and 

 hardly visible, and are known as blood shadows. They are 

 decolorized similarly by the action of electricity and continued 

 freezing. Tannic acid causes an extrusion of the haemoglobin 

 in small globules. Salt solution stronger than " normal " 

 causes a shrinkage of the cells from loss of water. They 

 become irregular in outline, small sharp projections appearing 

 everywhere; and are said to be crenated (Fig. 85, /). 



FIG. 85. 



Colored blood-cells (-</) and blood-platelets (hi. X 800. 

 a-c, red blood-cells of frog : a, seen from above ; 6, changed by addition of water ; 



c, seen from the side. 



d-g, red blood-cells of man : d, on deep focussing ; d\, on high focussing ; e,seen from 

 the side ; /, crenated ; 0, rouleau of blood-cells ; h, blood-platelets. 



Red blood-corpuscles have a considerable degree of elasticity, 

 so that they can be much changed by being forced through 

 narrow spaces and still regain their original shape. For 



