THE BLOOD. 71 



rounded by and mechanically inclosed within the outer wall of the 

 corpuscle. 



The red corpuscles have no nuclei, although in their usual state the 

 unequal refraction of transmitted light gives the appearance of a central 

 spot, brighter or darker than the border, according as it is viewed in or 

 out of focus. Their specific gravity is about 1088. 



Varieties. The red corpuscles are not all alike, some being rather 

 larger, paler, and less regular than the majority, and sometimes flat or 

 slightly convex, with a shining part apparent like a nucleolus. In 

 almost every specimen of blood may be also observed a certain number 

 of corpuscles smaller than the rest. They are termed microcytes, and 

 are probably immature corpuscles. 



It is necessary to take notice that much importance is attached to 

 one form of these smaller corpuscles 

 named blood plates by Bizzozero. They 

 are small, more or less rounded or 

 slightly oval granules, slightly if at all 

 colored, and about one-third the size 

 of ordinary colored corpuscles. From 

 them it is supposed the fibrin ferment 

 is specially derived. Some go so far as 

 t say that they are practically broken 

 up into it alone. They rapidly under- 

 go change in blood after it has been 

 drawn. They may form masses by co- 

 alescing. 



A peculiar property of the red ^Sl^SS'Sg^"'^ 

 corpuscles, which is exaggerated in 



inflammatory blood, may be here again noticed, i. e., their great ten- 

 dency to adhere together in rolls or columns, like piles of coins. These 

 rolls quickly fasten together by their ends, and cluster; so that, when 

 the blood is spread out thinly on a glass, they form a kind of irregular 

 network, with crowds of corpuscles at the several points corresponding 

 with the knots of the net (Fig. 66). Hence the clot formed in such a 

 thin layer of blood looks mottled with blotches of pink upon a white 

 ground, and in a larger quantity of such blood help, by the consequent 

 rapid subsidence of the corpuscles, in the formation of the buffy coat 

 already referred to. 



Action of Reagents. Considerable light has been thrown on the 

 physical and chemical constitution of red blood-cells by studying the 

 effects produced by mechanical means and by various reagents; the fol- 

 lowing is a brief summary of these reactions: 



Pressure. If the red blood-cells of a frog or man are gently 

 squeezed, they exhibit a wrinkling of the surface, which clearly indi- 

 cates that there is a superficial pellicle partly differentiated from the 



