1894.] MICROSCOPICAL JOURNAL. 99 



ter of blood ; so soft that they are flattened, elongated, 

 rolled np, or changed into various other shapes as they 

 rush along through the capillaries, yet so elastic that they 

 instantly resume their form when the pressure is removed. 

 They are of the highest necessity in the human economy, 

 both as oxygen carriers, and as forming material for con- 

 version into muscle, and hence on principle would be 

 least likely to suffer sudden changes in form or charac- 

 ter. When the blood is fresh, a small portion of a drop 

 can be taken up on a dissecting needle, the needle laid 

 flat on the cover glass, and drawn across it, leaving a 

 very tliin even film behind. This in my experience is the 

 best way of obtaining a single layer of corpuscles evenly 

 spread out. When the blood is dried in a clot on a board 

 or tool, or piece of cloth, the task is much more difficult. 

 The clot must be moistened by some fluid and the char- 

 acter of that fluid and its specific gravity are of the high- 

 est importance. On principle it is undoubtedly best to 

 use some fluid as nearly as possible in chemical composi- 

 tion to that of serum. Hence, solutions of mercuric bi- 

 chloride or even glycerine and water would seem to be 

 rather less suitable tlian those containing sodium chlo- 

 ride, sodic sulphate or albumen, as these substances are 

 natural constituents of the serum. 



The specific gravity of this macerating lluid should 

 not be less than about 1.050 to 1.055 as experience has 

 shown that the maceration of the corpuscles has a slight 

 tendency to enlarge them. Even a small variation in the 

 density of the fluid may exercise an appreciable influence. 

 There seems to be less power in the corpuscle when out 

 of the body to resist the influence of a strange fluid, than 

 when it is subject to the control of what is often called 

 the vital principle. Hence although the specific gravity 

 of the serum alone is about 1.028, it is not safe to use a 

 fluid of that specific gravity for softening up an old clot, 

 but the density should be about 1.050 — the specific grav- 



