178 The Microscope. 



tion will do admirably for a short study. When it begins to dry at 

 the edges a new preparation should be made. * 



On examination two kinds of cells are discovered, the red and 

 white blood-corpuscles. An inexperienced observer will have some 

 difficulty in finding the latter as the former are from three to twelve 

 hundred times more numerous. They should be looked for in the 

 open spaces. They are somewhat larger and granular, and, when 

 slightly out of focus, glisten with a pearl-like color. The student 

 should learn to distinguish at a glance the red from the white cells. 



Red blood corpuscles. The red cells will be seen, when magni- 

 fied about 400 diameters, to be round and disc-shaped. They show 

 a tendency to adhere together, forming rouleaux — rolls of coin — sug- 

 gesting the idea that they are sticky. Looking over the field a few 

 of them will be found on edge, they will then be seen to be bicon- 

 cave discs. This biconcavity of the cells gives them different 

 appearances when examined on the flat and at different foci. When 

 the focus is below the cell the center will appear light and the edge 

 dark, when above, the center is dark and the edge bright. This 

 latter view gives somewhat the appearance of a nucleus. The red 

 corpuscles are only red in the mass; individually they are a yellowish 

 color which is slightly greenish if the blood is venous. This color 

 is due to hamaglobin, which is evenly diffused through the cell. A 

 human red corpuscle is ab Dut ^o'y-Q of ^^ inch in diameter and about 

 Y^^Qo of an inch in thickness. Many cells will be iound somewhat 

 larger and, especially in certain diseased conditions, very much smaller. 

 Careful examination shows that the mammalian red corpuscle is 

 perfectly homogeneous, possessing neither nucleus nor limiting mem- 

 brane. Attempts have been made to demonstrate the presence of 

 one or both of these, but so far without success. All of these attempts 

 have called in the aid of reagents, many of them very powerful, 

 a dangerous procedure with such delicate material. It may be 

 mentioned in passing that the mammalian embryo contains nucleated 

 red corpuscles, but these disappear during later foetal life. 



Effects of reagents on the red corpuscles. Water causes the 

 corpuscles to swell up and assume a somewhat spherical form^ 

 Later the coloring matter is dissolved out and the cell becomes pale 

 leaving only the stroma behind. Alcohol, chloroform, acetic acid 

 and many other chemicals have a like effect on the hamaglobin. 

 When treated with the normal salt solution as well as with solutions 



* Poobain fresh human bloofl, twi^ta handkerchief around the finger until the end is- 

 congested. Then stab it li^hily with a sharp needle. If well done no discomfort will be 

 experienced and it can be repeated as often as necessary. 



