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 



