32 STRUCTURE OF RED CORPUSCLE. [BOOK i. 



a disc again on the removal of the dilution. If the serum be con- 

 centrated, the disc, giving out water, shrinks irregularly and assumes 

 various forms ; one of these forms is that of a number of blunted 

 protuberances projecting all over the surface of the corpuscle, which 

 is then said to be crenate ; in a drop of blood examined under the 

 microscope, crenate corpuscles are often seen at the edge of the 

 cover slip where evaporation is leading to concentration of the 

 plasma, or, as it should then perhaps rather be called, serum. In 

 blood just shed the red corpuscles are apt to adhere to each other 

 by their flat surfaces, much more than to the glass or other surface 

 with which the blood is in contact, and hence arrange themselves in 

 rolls. This tendency however to form rolls very soon diminishes 

 after the blood is shed. 



Though a single corpuscle is somewhat translucent, a compara- 

 tively 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 reflec- 

 tion 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 colourless 

 substance exhibiting under high powers an obscurely spongy or 

 reticular structure. These colourless thin discs seen flat-wise often 

 appear as mere rings. The substance composing them stains with 

 various reagents and may thus be made more evident. 



The red corpuscle then consists obviously of a colourless frame- 

 work, with which in normal conditions a red colouring matter is 

 associated; but by various means the colouring matter may be 

 driven from the framework and dissolved in the serum. 



The framework is spoken of as stroma ; it is a modified or 

 differentiated protoplasm, and upon chemical analysis yields pro- 

 teid substances, some of them at least belonging to the globulin 



