THE YOUNG SCIENTIST. 
123 
Microscopical Mistakes. 
ONE of the most common causes of mis- 
takes on the part of young micro- 
scopists is the presence of foreign sub- 
stances in the objects under examination. 
It is true that these things cause trouble 
chiefly to beginners with the microscope, 
but sometimes even experienced hands 
the greatest care. Ciiief amongst these 
are air bubbles, which present themselves 
as great round, black objects, which are 
sure to attract the attention of the young 
microscopist to the exclusion of every- 
thing else. Older observers pay no atten- 
tion to them. Then the lint from the 
cloths with which the slides are Aviped; 
POEEIGN SUBSTANCES LIABLE TO BE FOUND IN MICKOSCOPIC PKEPABATIONS. 
o. Cotton fibres. h. Flax fibres. c. Hairs. d. Air bubbles. e. Oil globules. 
/. Wheat starelL y. Potato stareli, li. Ilicc starch granules. 1,1,1. Vegetable 
tissue. k. Muscular fibres. /. Feathers. 
aL-e led astray. Beale, in his book, " How 
to Work with the Microscope," relates 
some curious and astonishing instances of 
this. 
There are certain things which are so 
universally present that they are liable to 
make their appearance in spite of the 
particles of dust from the air ; fragments 
of wool from carpets and clothes; dust 
and splinters from cork and wood ; bits of 
hair, feathers, leaves, etc., etc., are all 
liable to light on our work. In the ac- 
companying engraving we give the ap- 
pearence of a few of these things, and 
