28 
OF THE FREE DIATOM ACE AS. 
tap, Jc, leading into the funnel. The amount of disturbance, 
also, to which the Diatomaceas are subjected can be altered 
at will, by having mouth-pieces of different sizes made for the 
funnel tube, h, so that the apparatus is completely under 
the control of the operator, and any degree of washing can 
be given to the contents of the cylinder — the column of 
water issuing from the funnel and the opening of the 
mouth-piece below being made to bear a certain relation to 
each other. 
The Diatomacese being now cleansed from all impurities, 
the next step is to put them away in the herbarium. If 
the quantity be sufficient, it is a good plan to lay them 
(using a camel’s hair pencil for the purpose) on stout paper 
or cardboard, and there let them dry. Should they be 
wanted for examination under the microscope, it is easy to 
take up a portion, about the size of a pin’s head, and lay it 
on a glass slide. If, however, the original supply is small, 
the whole may be placed at once on a glass slide, protected 
by a thin glass covering. The advantage of this method is, 
that the object is always ready for microscopical observation 
and comparison, and the same preparation may be examined 
any number of times. Care, however, must be taken, 
while laying on the drop, that the individuals are not too 
crowded together, but that each one stands out distinctly ; 
otherwise the passage of light is interfered with, and a dark 
shapeless mass is all that meets the observer’s eye. 
The scientific value of each preparation is increased by 
having at hand some specimens in a 4 crude ’ state, that is 
to say, with the endochrome in situ, and not removed by 
an acid. The difference between these two states is this : 
when the valves have been submitted to the action of a 
strong acid, the delicate sculpturing of the silicious coat 
comes out, under proper illumination, in a marvellous 
way ; but the endochrome has entirely disappeared ; the 
plant is, in fact, a mere shell. In the other case, when 
the individuals are not submitted to an acid, and are 
examined in a fluid, the markings are scarcely visible ; 
