62 THE AMERICAN MONTHLY [Mar 
seems to be colorless, and we look through it and see ob- 
jects on the other side. But after a time while we look 
longer and longer at the water it becomes milky, as we 
say. It becomes faintly, shadowy and slightly opaque. 
Now what is this change due to? It becomes nebulous 
in fact and this nebulosity must be due to some change in 
the composition of the water as we know. 
It cannot be the same water that we have been looking 
at previously. It must be something else than water which 
has appeared, and this can be seen by placing a mass of 
water ina vessel at any time, but preferably in the spring 
and still more preferably when something has been dis- 
solved in it. A solution of hay is commonly used, and 
has been used for a long time when what is called “spon- 
taneous generation” is looked for. 
Now using a magnifying power of at least twelve hun- ~ 
dred diameters, 1-12th of an inch objective as it is com- 
monly called, with a No. 3 or B occular we have such a 
magnifying power,and we see that the nebulosity is caused 
by extremely fine organisms or seeming dots. They are 
in constant motion, not in one way, but trembling this 
way and that. They are what are called Monads. Monad 
is a term of D. F. Muller which Pritchard says in his His- 
tory of Infusorial Animalcules, 1852, are so named from 
its having been supposed to be the limit of animal organ- 
ization. First there appear masses of jelly-like extreme- 
ly small amebas. Let us see what Dr Leidy says about 
it for he gives the best account of amceeba that I can find. 
He says ‘‘it is an animal” when at rest, a spherical or oval 
mass of soft, hyaline, colorless, homogeneous, pale, gran- 
ular protoplasm, possessing extensile and contractile 
power, and in the active condition devoid of an investing 
membrane, or any kind of covering. This is all. It is in 
motion when we see it, but motionless when first found. 
Let us imagine a drop of the white of an egg, any kind 
of egg, be it animal or vegetable or protiston. For that 
