MANIPULATION OF THE MICROSCOPE. 37 
are often set up in the mounting medium which may be 
misinterpreted. A still more serious source of error lies 
in the phenomenon known as the Brownian movement, 
or pedesis, a dancing, oscillating motion which affects 
suspensions of finely divided solid particles under cer- 
tain not very clearly understood conditions. Gamboge 
or carmine suspended in water shows the Brownian 
movement well, and should be studied carefully in order 
that such motion may not be confused with that charac- 
teristic of the bacteria or other living organisms. 
REFERENCES. 
BauscH, E. Manipulation of the Microscope. Rochester, 1901. 
GacE, S.H. The Microscope. Ithaca, N. Y., 1904. 
