214 



FUNCTIONS OF NUTRITION. 



FIG. 44. 



RED GLOBULES OP THE BLOOD, adhering to- 

 gether, like rolls of coin. 



through the narrow channels and currents, often seen in a drop of 

 blood under microscopic examination ; but they regain their original 

 shape as soon as the pressure is taken off. 



So far as observation can determine, the red globules of the blood, 



in man and mammalians, are 

 homogeneous in structure; 

 showing no distinction between 

 an external envelope and the 

 parts within. Although some 

 microscopists of high repute 

 (Kb'lliker, Richardson) continue 

 to regard the existence of an 

 exterior membrane as probable, 

 it is not generally admitted, and 

 cannot be directly demonstrated. 

 Each globule appears like a mass 

 of organic substance of the same 

 color, consistency, and composi- 

 tion throughout. 



The blood-globules are altered 

 by various physical and chemi- 

 cal agents. If a drop of blood 

 under the microscope be not protected from evaporation, the globules 

 near the edges of the preparation often diminish in size, becoming 

 shrivelled and notched at their margins ; an effect apparently due to 

 the partial loss of their watery ingredients. This alteration some- 

 times takes place with great rapidity in blood withdrawn for exami- 

 nation; but, according to Kol- 

 liker, it is never seen in the 

 blood while circulating in the 

 vessels. 



If water, on the other hand, 

 be added to the blood, the red 

 globules absorb it by imbibition, 

 lose their central concavity, as- 

 sume the spherical form, and 

 become paler. A large quan- 

 tity of water may completely 

 extract the coloring matter, 

 leaving the globules as pale, 

 colorless circles, almost invis- 

 ible from their tenuity. In 

 this condition they may again 



be brought into View by add- RED GLOBULES OF THE BLOOD, shrunken, with 



their margins notched. 



ing an iodine solution, which 



stains them of a yellowish color. If water be added in quantity 



just sufficient to be imbibed by the globules, without extracting 



FIG. 45. 



