418 



THE BLOOD 



[CH. XXVI. 



The Blood-Corpuscles. 



There are two principal forms of corpuscles, the red and the 

 white, or, as they are now frequently named, the coloured and the 

 colourless. In the moist state the red corpuscles form about 40 per 

 cent, by weight of the whole mass of the blood. The proportion of 

 colourless corpuscles is only as 1 to 500 or 600 of the coloured. 



Red or Coloured Corpuscles. Human red blood corpuscles are 

 circular biconcave discs with rounded edges, -j^Vo- inch in diameter 

 (7/ui to S/UL) and T 2ihnr i ncn > or about 2/z, in thickness. When viewed 

 singly they appear of a pale yellowish tinge ; the deep red colour 

 which they give to the blood is observable in them only when they 

 are seen en masse. 



FIG. 347. Corpuscles of the frog. The 

 FIG. 346. Red corpuscles in rouleaux. The central mass consists of nucleated 



white corpuscles are uncoloured. coloured corpuscles. The other cor, 



puscles are two varieties of the 

 colourless form. 



According to Rollett they are composed of a transparent filmy framework 

 infiltrated in all parts by the red pigment hcemoglobin. This stroma is elastic, so 

 that as the corpuscles circulate, they admit of change in form, and recover their 

 natural shape as soon as they escape from compression. According to this theory, 

 the consistency of the peripheral part of the stroma is greater than that of the 

 central portions ; the outer layer thus plays the part of a membrane in the processes 

 of osmosis that occur when water or salt solutions are added to the corpuscles. 

 This view of Rollett has been questioned, particularly by Schafer, who regards the 

 red corpuscles as composed of a colourless envelope enclosing a solution of haemo- 

 globin. The presence of a membrane on the exterior of the corpuscle is undoubted, 

 and can be clearly distinguished by a good microscope in the larger corpuscles of 

 amphibia. It is, however, difficult to explain the elasticity of the corpuscles, and 

 the central position of the nucleus in nucleated red corpuscles, unless we also assume 

 that delicate fibres pass across the interior of the corpuscles. 



Mammalian red corpuscles have no nuclei ; the unequal refraction 

 of transmitted light gives the appearance of a central spot, darker or 

 brighter than the border, according as it is viewed in or out of focus. 

 Their specific gravity is about 1088. 



