34 6 



THE POPULAR SCIENCE MONTHLY. 



sans that are working there 



When I watched the ducks swimmino- 

 in the old trough, little did I think of the noiseless hands that were 

 building up those velvety-green walls, or of the unseen and unnum- 

 bered fleet of boats sculling through the water. 



Young folks have a great fancy for " bloody stories ; " so I am going 

 to tell you not exactly a "bloody story," but a story about blood, and 

 you need not be alarmed, for before I finish you will find there is 

 nothing in blood to alarm any one, but a great deal that is useful, 

 curious, and beautiful. If you prick your finger with a needle, and 

 squeeze out a drop of blood and place it under the microscope, you will 

 be astonished at what you see (Fig. 14). You can hardly believe that 

 a drop of blood contains so many curiosities. First you observe a whole 

 lot of little reddish-looking bodies, and among these a number of larger 

 transparent bodies, which look like minute splashes of light-colored jel- 

 ly. It is about these jelly-like bodies I am going to talk with you. If 



Red cell, seen 

 on its edge. 



-- Anicebse. 



Red cells. 



. Amceba, or 

 colorless cell. 



Fig. 14. Blood-Cells, colored and colorless. 



Figs. 15 and 16. The Aukeba or 

 Blood-Cell changing its Form. 



you keep your eye on one of them, you see that it continually changes 

 its form, and that it has a slow, crawling kind of motion ; and, if you 

 try to make a drawing of it on paper, your picture will never be twice 

 alike (Figs. 15, 16). It puts out something from one side which looks 

 like a foot ; then it draws in this foot, and puts out another at the other 

 side, as if trying to find a soft place to walk upon. Sometimes it puts 

 out several of these feet at one time. This little jelly-splash appears to 

 use its feet as we use ours, to walk with, though you see it gets on quite 

 slowly aud awkwardly. Its foot is called a pseudopodium, which means 

 false foot. These little bodies have a very suitable name amoebae, 

 and the w r ord means changing. This name was given to them, no 

 doubt, because they are constantly changing their form. The amoeba, 

 or blood-cell, is larger than the still protococcus, or moiild of the paling, 

 and not quite as large as the moving protococcus, or green water- 

 mould. It is usually about -g-gVo f an nicn in breadth. It does not 

 possess the cellulose or woody sac, like the little protococcus houses. 

 It is more like the pear-shaped protococcus boatmen. Its wall is just 

 the hardened outer layer of the jelly or protoplasm. It has no thin 



