198 BACTERIOLOGICAL DIAGNOSIS. 
In the older methods of fixing sections to the slides 
various forms of cements had to be used, and were a 
great disadvantage. They are quite unnecessary except 
for sections of the central nervous system; if these are 
being dealt with the slide must be coated with a very 
thin layer of a solution of egg-albumen in water before 
the section is laid upon it. The process is then exactly 
the same as before. 
STAINING AND MOUNTING PARAFFIN 
SECTIONS. 
We will suppose that the sections have been cut, 
flattened out on hot water, and caused to adhere to 
slides, and shall describe in general terms the steps 
through which they must be taken before they are 
ready for examination. In the first place, it is obvious 
that the paraffin which permeates all parts of the section 
and surrounds it on all sides must be removed; and this 
is done by pouring xylol, benzine, or turpentine upon it. 
At least two supplies of the fluid should be used, and it 
should be allowed to act for at least two minutes, the 
slide being rocked all the time. We have now removed 
the paraffin, and the next step is to remove the xylol or 
other solvent; this is done by means of absolute alcohol. 
At least two lots should be used, and it should be 
allowed to act for two minutes. The slide is then 
washed in water, and is ready for staining. When 
the section is wet with xylol it will be quite transparent; 
this is because the refractive index of the xylol is almost 
the same as that of glass and the rays of light which 
come through the section are not bent. But when the 
