THE COKPUSCLES OF THE BLOOD. 39 



light in passing through them, when they are examined by transmitted light, 

 are more refracted at the rim than in the centre. The effect of this is that, 

 when viewed at what may be considered the proper focus, the centre of a 

 corpuscle appears clear, while a slight opacity marks out indistinctly the 

 inner margin of the thicker rim, whereas, when the focus is shifted either 

 up or down, the centre becomes dark and the rest of the corpuscle clear. 

 Any body of the same shape, and composed of substances of the same 

 refractive power, would produce the same optical effects. Otherwise the 

 corpuscle appears homogeneous, without distinction of parts and without 

 a nucleus. A single corpuscle seen by itself has a very faint color, look- 

 ing yellow rather than red, but when several corpuscles lie one upon the 

 top of the other the mass is distinctly red. 



The red corpuscle is elastic, in the sense that it may be deformed by 

 pressure or traction, but when the pressure or traction is removed regains its 

 previous form. Its shape is also much influenced by the physical conditions 

 of the plasma, serum, or fluid in which for the time being it is. If the 

 plasma or serum be diluted with water, the disc, absorbing water, swells up 

 into a sphere [Fig. 7], becoming a disc again on the removal of the dilution. 

 If the serum be concentrated, the disc, giving 

 out water, shrinks irregularly and assumes [FIG. 7. 



various forms ; one of these forms is that of a a 6 c d e 

 number of blunted protuberances projecting all k tfk JF?| f^\ 

 over the surface of the corpuscle, which is then J |p Jp *"* ^^ 

 said to be crenate ; in a drop of blood examined 

 under the microscope, crenate corpuscles are ^ ^W 

 often seen at the edge of the cover-slip where "%if 9 C& 



evaporation is^ leading to concentration of the a _ e> successive effects of water 

 plasma, or, as it should then perhaps rather be upon a red corpuscle; /, effect of 

 called, serum. In blood just shed the red cor- solution of salt, crenated; g, effect 

 puscles are apt to adhere to each other by their of tannic acid.] 

 flat surfaces, much more than to the glass or 



other surface with which the blood is in contact, and hence arrange them- 

 selves in rolls. This tendency, however, to form rolls very soon diminishes 

 after the blood is shed. 



Though a single corpuscle is somewhat translucent, 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 deprived of fibrin) 

 is frozen and thawed several times it changes color, 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 previously 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. 



When laky blood is allowed to stand a sediment is formed (and may be 

 separated by the centrifugal machine) which on examination is found^ to 

 consist of discs, or fragments of discs, of a colorless substance exhibiting 



