TOOLS AND METHODS OF WORK 29 



Place a drop of the solution on the slide and smear it evenly over 

 the surface, and then wipe as much off as possible either with the hand 

 or with a clean piece of non-linty cloth. Now place a few drops of 

 water on the slide, or float the section on to it, warm gently over the 

 spirit lamp, when the paraffin and the section will become smoothed out 

 and free from wrinkles. Now tilt the slide and allow the water to drain 

 off, guiding the sections into position with a needle while doing so. The 

 slide should now be placed in the warm incubator for an hour or two to 

 dry. The paraffin may now be removed by gently heating the slide 

 over the spirit lamp to the melting point of the paraffin, and placing 

 direct into xylol, which completes the operation by dissolving out all 

 traces of paraffin, and by the heating operation the albumen will be 

 coagulated, and the section cemented on the slide. 



The slide with the sections should now be rinsed in one or two 

 changes of alcohol and it is ready for staining. After staining, place the 

 slide in xylol for ten minutes to clarify the section, drain off the surplus 

 xylol, and mount the section in "xylol balsam." 



Staining. 



The art of staining consists in differentiating the various tissues of 

 which plants and animals are composed, the operations being governed 

 by the chemical affinities of the tissues to be stained, and these vary 

 considerably in accordance with the age of the tissues themselves. No 

 tissue will take up a stain unless there is an affinity between the tissue 

 and the stain, and no simple tissue will take up two stains unless the 

 cells composing it are nucleated. A preparation composed of two or 

 more tissues may be stained in two or more colours, but two or more 

 colours cannot be put into a preparation unless there is a tissue for each 

 of them, for example, developing vegetable tissue may be differentiated 



