94 BLOOD A.\D LYMPH. 



on the entire corpuscle, or only a few ; or a large number 

 studding the surface of the much-shrivelled spherical cell. 

 The more the cell is contracted the greater is the number of 



spines. 



Crenation is caused by contraction of the corpuscle from 

 loss of part of its fluid contents through osmosis, and occurs 

 when the density of the plasma is increased by evaporation 

 from exposure to the air or by the addition of saline or other 

 substances. 



Other changes of form : When the density of the plasma 

 is diminished, as by the addition of water, the red corpuscles 

 through osmosis absorb fluid, swell, and become spherical, and 

 at the same time lose their color, the haemoglobin in the 

 corpuscles leaving them and passing into solution in the 

 plasma outside. 



Sometimes the substance of the corpuscles shrinks, leaving 

 artificial empty spaces or vacuoles. 



In squeezing blood from a puncture in the skin, portions of 

 the corpuscles are often broken off, and, assuming a rounded 

 form, appear like diminutive corpuscles. 



At other times the corpuscles appearyferer?, twisted, or doubled 

 up in the form of a hemispherical bowl. 



Familiarity with the changes of form which red corpuscles 

 undergo under changed conditions is necessary to avoid mis- 

 taking them for morphologic or pathologic abnormalities. 



In various disease-conditions interesting variations from the 

 normal are exhibited by red corpuscles, as the presence of 

 nuclei, and abnormalities in size, coloration, and consistency. 



The function of the red blood-corpuscles is to convey oxygen 

 from the lungs, whSre it is taken up by the hemoglobin, to 

 the tissues, where it is given out for nutritive purposes. 



In structure they appear to consist of a pliable and elastic 

 colorless proteid stroma, in which haemoglobin is suspended in 

 solution ; the form and consistency of the cells are due to the 

 stroma, the color, to the haemoglobin. They do not exhibit 

 ameboid movement or cell division. Considering their lack 

 of nuclei, and of other vital properties, the red blood-corpus- 

 cles must be regarded as a very degenerate form of cell, 

 exhibiting few characteristics of vitality and serving the 

 purely mechanical purpose of carrying oxygen. 



