150 



The Preparation of Microscope Slides 



Fig. 113. Laying out the ribbon. 



and it is usually safe to allow at least 10 and sometimes 20 per cent for 

 expansion when the sections are finally flattened. The ribbon should 

 never be cut completely until a sample has been flattened on a slide, in 

 order that one may judge the degree of expansion. Although the sections 

 shown in Fig. 115 are mounted on an ordinary 3- by 1-in. slide, it would 

 be more practical for a ribbon as wide as this to use a 3- by 1% -in. or 

 even a 3- by 2-in. slide. The sections should never occupy the whole area 

 of the slide. At least % in. should be left at one end for subsequent label- 

 ing. When the decision has been made as to how many sections shall be 

 left in each piece of ribbon, the first row of ribbons is cut into the 

 required lengths (Fig. 114). Then the worker must decide what shall be 

 used to cause them to adhere to the slide. It is conventional to use: 



Mayer's Albumen: 



Fresh egg white 50 ml 



Glycerin 50 ml 



Sodium salicylate 1 g 



The author prefers to dilute the selected adhesive two or three hundred- 

 fold with water and to use this diluted adhesive in the next operation of 

 flattening the sections. However, the adhesive can be made full strength 



