68 MATERIALS AND PROCESSES OF SLIDE-MAKING 



immediately. If this procedure is desired, shake the ingredients together until 

 they are thoroughly mixed. Filter. Apply a thin smear of this on a clean slide 

 with the tip of the little finger. 



It will have been apparent to the worker from the moment he started cut- 

 ting the sections that they are not absolutely flat. They may be slightly crinkled 

 or slightly distorted and, therefore, must be flattened by being warmed on water 

 heated just below the melting point of the wax. Some people place this water 

 on the slide and then add the sections to it, but the author prefers to lay the 

 ribbons on the slide as shown in Fig. 41. This is not nearly as easy as it looks. 

 The tips of two brushes should be moistened with the tongue just enough to 

 bring the hairs to a point. Then the two moist points are delicately touched 

 (too much pressure will cause the ribbon to adhere to the paper) to each end 

 of the selected piece of section. This piece is lifted as shown in the illustration 

 and placed on the slide. When a sufficient number of pieces of ribbon have 

 been accumulated, the slide is picked up carefully, reversed, and laid on top 

 of the last three fingers of the left hand exactly as shown in Fig. 42. It is 

 quite fatal to grasp the slide by the sides; if this is done when the water is 

 flooded on from the pipette, the meniscus coming to the edge of the slides 

 will break against the fingers, causing the sections to adhere to the fingers 

 permanently. The manner shown is quite safe. The water containing "the ad- 

 hesive (if none has been applied to the slide) is flooded on from a pipette as 

 illustrated. Plenty of fluid should be applied and should be raised in quite a 

 sharp meniscus from the edge of the slide. 



The sections must now be flattened. This is much better done rapidly with 

 a flame than slowly on a hot plate. Fig. 43 shows the slide held over a small 

 alcohol lamp, but a micro-bunsen can be employed equally well. The slide 

 should be exposed to heat for a moment, withdrawn to give time for the heat 

 to pass from the glass to the fluid, rewarmed, 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 permitted to melt, it will be difficult later, if not impossible, to 

 cause the sections to remain attached to the glass. As soon as the sections are 

 flattened, the slide is gently tilted backward toward the hand to run off the 

 excess water against the thumb, leaving the sections stranded in place. The 

 slide is usually placed on a thermostatically controlled hot plate (seen in Fig. 

 52) and permitted to dry. Most people leave their slides overnight, but fre- 

 quently an hour would be sufficient. Dryness can be gauged without the least 

 trouble by the fact that a moistened slide shows the wax to be more or less 

 opalescent, while on a properly dried slide it is almost glass-clear. 



The method just described is susceptible of several variations, which may 



