32 STRUCTURE OF RED CORPUSCLE. [BOOK i. 



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

 concentrated, 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 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 exami- 

 nation 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 



