ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
163 
into its position on the slide with a stiff brush, and the process is 
repeated with one ribbon after another until the slide is full. With a 
little practice one soon learns how to bring the rows close together so 
that no space is wasted. The slide is then set up on end to allow the 
superfluous water to drain off. 
The best dish for carrying out this process is, perhaps, a flat glass 
dish standing on a dark table, as the manipulation is more easily 
accomplished when the white paraffin is thus thrown up in relief. The 
temperature of the water is of course important, but as different workers 
use paraffins of varying hardness, no absolute rule can bo laid down. 
It should be comfortably warm to the hand, but never so warm as to 
melt the soft paraffin holding the sections together. Short of this, 
however, the warmer the water the more rapidly and completely aro the 
sections flattened. 
So far the sections are simply lying loose upon the slide, and they 
have yet to be fixed to it. This is done by evaporating the water from 
the surface of the slide. The evaporation might be carried out in many 
ways, but I shall best explain it by describing my own practice. I 
almost invariably use paraffin for imbedding whoso melting-point is 
52° C., and the imbedding oven, an ordinary copper one, is therefore 
kept at about 54° C. or 55° C. The slides, after the water has 
drained off as much as possible, are placed on the top of the oven, 
where the temperature is probably a little under 5(P C., and where, 
consequently, the paraffin of the sections is not melted, though the water 
rapidly evaporates. The slides are kept there, with a cardboard cover 
over them to keep off dust, until the evaporation is complete, and the 
sections have adhered to the slide. The time required for this varies, 
as I shall show immediately ; but the important point is that the paraffin 
must never be melted until the last trace of water has disappeared from 
the slide. If this premature melting happens by any accident, the 
sections are certain to peel off later. When the water has evaporated 
completely, the opacity of the sections disappears, they become much 
more transparent, and they look dry. A very few experiments enable 
one to be sure of the point when slides are safe. Of course when the 
paraffin used for imbedding is of a lower melting-point than 52° C., the 
temperature for evaporation must also be lower ; and when the oven is 
regulated as above, this can be managed by putting a few thicknesses of 
paper under the slide. 
When the fixation is comjilete, the paraffin is molted by putting the 
slide inside the oven for a little, and is then washed off with turpentine 
or xylol ; and, if the piece of tissue has been stained en bloc, the sections 
can be mounted at once in balsam. 
One of the great advantages of this method is the perfect ease and 
safety with which it allows sections on the slide to be manipulated, so 
that the most various stains and reagents can be applied successively to 
a slide, e. g. the complicated processes used to demonstrate bacteria in tho 
tissues can be applied, with the certainty, moreover, that there is nothing 
on the slide to be stained which was not in tho section. 
The time required for complete fixation varies in dependence on 
several circumstancos, but of these the most important are the thorough- 
ness with which the superfluous water has been drained off the slide, and 
