216 THE BLOOD. 



compressing the globules, forces them into such a position that they 

 may occupy the least possible space. This position is evidently 

 that in which they are applied to each other by their flat surfaces, 

 as above described. 



The color of the blood-globules, when viewed by transmitted 

 light and spread out in a thin layer, is a light amber or pale yellow. 

 It is, on the contrary, deep _ red when they are seen by reflected 

 light, or piled together in comparatively thick layers. When viewed 

 singly, they are so transparent that the outlines of those lying under- 

 neath can be easily seen, showing through the substance of the 

 superjacent globules. Their consistency is peculiar. They are not 

 solid bodies, as they have been sometimes inadvertently described ; 

 but on the contrary have a consistency which is very nearly fluid. 

 They are in consequence exceedingly flexible, and easily elongated, 

 bent, or otherwise distorted by accidental pressure, or in passing 

 through the narrow currents of fluid which often establish them- 

 selves accidentally in a drop of blood under microscopic examina- 

 tion. This distortion, however, is only temporary, and the globules 

 regain their original shape, as soon as the accidental pressure is 

 taken off. The peculiar flexibility and .elasticity thus noticed are 

 characteristic of the red globules of the blood, and may always 

 serve to distinguish them from any other free cells which may be 

 found in the animal tissues or fluids. 



In structure the blood-globules are homogeneous. They have 

 been sometimes erroneously described as consisting of a closed 

 vesicle or cell-wall, containing in its cavity some fluid or semi-fluid 

 substance of a different character from that composing the wall of 

 the vesicle itself. No such structure, however, is really to be seen 

 in them. Each blood-globule consists of a mass of organized ani- 

 mal substance, perfectly or nearly homogeneous in appearance, and 

 of the same color, consistency and composition throughout. In 

 some of the lower animals (birds, reptiles, fish) it contains also a 

 granular nucleus, imbedded in the substance of the globule ; but 

 in no instance is there any distinction to be made out between an 

 external cell- wall and an internal cavity. 



The appearance of the blood-globules is altered by the addition 

 of various foreign substances. If water be added, so as to dilute 

 the plasma, the globules absorb it by imbibition, swell, lose their 

 double central concavity and become paler. If a larger quantity 

 of water be added, they finally dissolve and disappear altogether. 

 When a moderate quantity of water is mixed with the blood, the 



