SEC. 2. THE CORPUSCLES OF THE BLOOD. 



The Red Corpuscles. 



§ 24. The redness of blood is due exclusively to the red 

 corpuscles. The plasma as seen in thin layers within the living 

 blood vessels appears colourless, as does also a thin layer of serum ; 

 but a thick layer of serum (and probably of plasma) has a faint 

 yellowish tinge due as we have said to the presence of a small 

 quantity of a special pigment. 



A single red corpuscle seen by itself under the microscope is 

 a fairly homogeneous, imperfectly translucent biconcave disc of a 

 very faint colour, looking yellow rather than red ; but when several 

 corpuscles lie one upon the top of the other the mass appears 

 distinctly red ; and though a single corpuscle is somewhat trans- 

 lucent, a comparatively thin layer of blood is opaque ; type for 

 instance cannot be read through even a thin layer of blood. 



When a quantity of whipped blood (or blood otherwise de- 

 prived of fibrin) is frozen and thawed several times it changes 

 colour, becoming of a darker hue, and is then found to be much 

 more transparent, so that type can now be easily read through a 

 moderately thin layer. It is then spoken of as laky blood. The 

 same change may be effected by shaking the blood with ether, or 

 by adding a small quantity of bile salts, and in other ways. Upon 

 examination of laky blood it is found that the red corpuscles are 

 ' broken up ' or at least altered, and that the redness which pre- 

 viously was confined to them is now diffused through the serum. 

 Normal blood is opaque because each corpuscle while permitting 

 some rays of light (chiefly red) to pass through, reflects many 

 others, and the brightness of the hue of normal blood is due to 

 this reflection of light from the surfaces of the several corpuscles. 

 Laky blood is transparent because there are no longer intact 

 corpuscles to present surfaces for the reflection of light, and the 

 darker hue of laky blood is similarly due to the absence of 

 reflection from the several corpuscles. 



