RED CORPUSCLES. 143 



dark if the objective is raised (Fig. 167, C). The biconcave shape is appar- 

 ent when a corpuscle is seen on edge (Fig. 167, B). This form of the red 

 corpuscles is still ordinarily described as normal, since it is observed in 

 freshly drawn blood. The making of the thin layer has, however, sub- 

 jected the blood to very unnatural conditions. Very quickly the corpuscles 

 arrange themselves in rows, or rouleaux (Fig. 173), such as are not found 

 within the blood vessels. In most of the sections which the student 

 examines, in preparing which various preserving fluids have been used, 

 cup shaped corpuscles will be seen like those in Fig. 167, D. Often they 

 will show irregular contractions and distortions (E). If the corpuscles 

 are placed in a dilute fluid, their haemoglobin is dissolved out and water 

 enters them. They become mere flattened membranes or shadows (Fig. 

 167, F). Such barely visible structures are sometimes found in urine. In 

 dense solutions, or in ordinary fresh preparations as they begin to dry, 

 water leaves the corpuscle, which shrinks, producing nodular, refractive 

 masses of haemoglobin called crenated corpuscles (Fig. 167, G). A 0.6% 



4 



FIG. 168. 



I, Haemin crystals and 3, haematoidin crystals from human blood; 2, crystals of common salt ( X 560) ; 

 4, haemoglobin crystals from a dog (X 100). 



aqueous solution of common salt is said to cause the least distortion 

 from swelling or shrinkage. In life, corpuscles presumably change their 

 shape with variations in the plasma and in the nature of the haemoglobin. 

 A small number of spherical corpuscles is said to occur normally. When 

 a drop of blood is heated to excess the corpuscles form small globules 

 united by stalks or entirely separate. This indicates a viscid membrane, 

 but does not prove the entire absence of membrane as has been asserted. 

 In strong picric acid the corpuscles burst, discharging their contents 

 through a rent in a capsule which may be largely due to the reagent. 



Haemoglobin is an exceedingly complex chemical substance which 

 combines readily with oxygen to form oxyhaemoglobin. To the latter the 

 bright color of arterial blood is due. Venous blood becomes similarly red 

 on exposure to air. Through the oxyhaemoglobin, oxygen is transferred 

 from the lungs to the tissues. Haemoglobin may be dissolved from the 

 corpuscles by mixing blood with ether, and upon evaporation it crystallizes 

 in rhombic shapes which vary with different animals. Those from the 

 dog are shown in Fig. 168, 4; in man they are also chiefly prismatic. Haemo- 



