118 



THE ART OF MAKING MICROSCOPE SLIDES 



Flattening 



It is fatal to grasp the slide by the sides; 

 if this is done, when the water is flooded 

 on from the pipet, the meniscus coming 

 to the edge of the sUdes will break against 

 the fingers, to which the sections will 

 permanently adhere. The technique shown 

 is quite safe and the water containing the 

 adhesive (if none has been applied to the 

 shde) is then flooded on froni a jiij^et in 



tened, the slide is gently tilted backward 

 towards the hand so as to run off the 

 excess water against the thumb, leaving 

 the sections stranded in place. The sUde 

 is now usually placed on a thermostati- 

 cally controlled hot plate (seen at the back 

 of Fig. 78) and dried. Most people leave 

 their shdes overnight but frequently an 

 hour would be sufficient. Dryness can be 



Fig. 69. Flooding the ribbons. 



the manner shown. Enough fluid should 

 be appHed to raise a sharp meniscus at 

 the edge of the shde. 



The sections must now be flattened, and 

 this is better done rapidly with a flame 

 than slowly on a hot plate. Fig. 70 shows 

 the shde being held over a small alcohol 

 lamp, but a micro-bunsen can be em- 

 ployed equally well. The shde should be 

 exposed to heat for a moment, withdrawn 

 to give time for the heat to jiass from the 

 glass to the fluid, warmed again, and so 

 on, until the sections are observed to be 

 flat. The utmost care must be taken at 

 this point for, if the paraffin is i)ermitted 

 to melt, the sections will not stick to the 

 glass. As soon as the sections are flat- 



gauged without the least trouble by the 

 fact that a moist shde shows the wax to be 

 more or less opalescent, while on a prop- 

 erly dried shde it is almost glass-clear. 



The method just described is susceptible 

 of several variations which may be briefly 

 noticed. Some people do not drain the 

 water from the slide, nor do they heat 

 the slide over the lamp; they merely place 

 the slide, as soon as the water has been 

 added to it, on the thermostatically con- 

 trolled hot plate so that the sections dry 

 and flatten at the same time. The objec- 

 tion to this procedure is that dissolved air 

 in the water used for flattening usually 

 comes out in the form of bubbles which 

 accumulate under the section, either cans- 



