84 NORMAL HISTOLOGY. 



The nuclei of these cells become visible on the 

 application of a variety of agents which determine 

 the death of the cells, such as acetic acid, dilute 

 alcohol, and certain coloring agents. The cells vary 

 greatly in size, but on the average are, in man, 

 larger than the red cells. 



2. Red Blood-cells. These cells, having in man the 

 form of bi-concave discs, consist apparently, simply 

 of a cell-body without membrane or nucleus. Al- 

 though when crowded together in great numbers 

 they give the blood a distinct red color, when seen 

 singly they have a greenish-yellow tint. The cell- 

 body is very soft and pliable, jelly-like, changing its 

 shape on the slightest pressure. It is more deeply 

 colored at the periphery, when seen from the side, 

 because of its greater thickness at that part. Owing 

 to the peculiar shape of the cell, it acts as a lens 

 upon the light passing through it, and its central 

 portion is either light or dark, depending upon 

 whether the objective is approached to or with- 

 drawn from it. When examined fresh in the plasma, 

 many of the cells arrange themselves closely to- 

 gether side by side, in longer and shorter rows. 



If water is mixed with blood, the red cells soon 

 begin to swell and lose their color. Sometimes 

 one side swells faster than the other and the 

 cells become cup-shaped : finally they become 

 globular, are considerably larger than at first, and 

 colorless. 



