CH. VII} 



PARAFFIN SECTIONING 



187 



extension is almost always accomplished on the slide itself. A slide is albumen- 

 ized ('i 290) and the ribbon cut into short pieces and placed on the slide. Distilled 

 or filtered water is then added with a pipette (Fig. 147) until the sections float. 

 Then the slide is moved back and forth over an alcohol or gas flame to warm the 

 water. Care must be taken to avoid melting the paraffin. As the water warms 

 the paraffin containing the sections will flatten and stretch out. One will be sur- 

 prised at the amount of extension. It is necessary to take pieces considerably 

 shorter than the cover-glass to be used or when extended the sections will not all 

 be covered. After the sections are extended, arrange the ribbons carefully on the 

 slide as shown in Fig. 162 if one is making serial sections. Arrange in the middle 

 of the slide if only one or two sections are on each slide (Fig. 138). Let the ex- 

 cess water drain off. Now let the slide stand several hours for the water to evapor- 

 ate completely. The time will depend on the temperature and the dryness of the 

 atmosphere. If there is plenty of time, leave the slides 24 or 48 hours. If one 

 has a register with hot air intake, the slides may be put in the current of hot air. 

 They will dry out in half an hour or an hour. Sections which have been left for a 

 vear have given excellent results. 



Fig. 157. Trays for slides and for ribbons of sections. The figures show the 

 construction. It is important to have the bordering f tame with rounded corners so 

 that the trays may be easily pulled out of a pile or reinserted. The screw eye shown 

 in A makes it easy to pull out a single tray. For ribbons of sections a piece of paper 

 is placed in the tray and the ribbons are placed on it. (A) Face view, (B) Sec- 

 tional view of the whole tray, (C) Sectional view of one side to show the construc- 

 tion more clearly. Trays of this kind are so cheap {$15.00 pet hundred for those 

 holding 50 to 60 slides), that a laboratory can have a great number. (Trans. Amer. 

 Micr, Soc, 1899, p. 107). 



The slide trays (Fig. 157) are excellent for drying preparations of all kinds. 

 \ 290. Fastening the Sections to the Slide. — To fasten the sections firmly 

 to the slide, coat the slide with albumen fixative (§ 312) as follows : Put a minute 



