RED BLOOD-CORPUSCLES. 93 



they are homogeneous throughout, and they possess no cell- 

 envelope. They contain no nuclei, except in early embryonic 

 life and in abnormal conditions. Their color, when seen 

 singly or in thin layers, is not red, as the name indicates, but 

 a characteristic pale yellow with a slight greenish tinge ; it is 

 only in mass that they produce the effect of red color. They 

 are soft, elastic, pliable, almost gelatinous. As they flow 

 through the capillaries or move in currents in the micro- 

 scopical specimen they change shape with the least pressure, 

 and may become greatly distorted ; but on release from re- 

 straint they resume their normal discoid shape. 



The number of red corpuscles in given volumes of blood 

 under similar normal conditions is practically constant, and 

 near the sea-level in adult males 

 is about 5,000,000 in each cubic FIG. 40. 



millimetre of blood ; in females, 

 about 4,500,000. In very vigor- 

 ous individuals the number of 

 red corpuscles may be increased, 

 even up to 6,000,000; while 

 with increase of altitude above 

 sea-level there is a very marked 

 increase in their number. 



When a drop of blood is 

 placed under the microscope the 

 red corpuscles are observed to 



i ., ., l (> ,. i Red blood-corpuscles of man. a, sur- 



exhlblt, for a time, a tendency face view of normal corpuscles; 



to form rouleaux-that is, they kgg^&SSr&S?^ 

 become arranged or adherent ; & ; < ^g 



together evenlv Side DV Side, of broken corpuscles ; g, bent and 



Ti T / . distorted corpuscles: h. swollen 



like a pile OI COins. and decolorized corpuscle. 



Crenation : The red corpuscles 



are so delicately adjusted to the blood-plasma that they are 

 very easily affected as to shape by any alteration in the 

 density and composition of the medium in which they occur. 

 One of the commonest of these change's is crenation. This 

 consists of a shrinkage of the corpuscle, which loses its dis- 

 coid shape and becomes spheroidal or irregularly distorted, 

 while at the same time minute rounded or spiny projections 

 appear on the surface ; of these spines there may be only one 



O-C ; 



