CH. XI] PREPARATIONS BY THE PARAFFIN METHOD 



383 



formed, viz. : the sections are made smooth and they are also fastened 

 to the slide. Put a minute drop of albumen fixative on the middle 

 of a slide and with the ball of one finger spread it over the slide, 

 making a thin even layer. It cannot be too thin. It is liable to 

 stain if it is too thick. 



With a pipette (fig. 234) put several drops of water on the slide 

 and then place a piece of ribbon 

 6n the water ; or put the sections 

 on the albumenized slide and add 

 the water afterward. Heat the 

 slide carefully over a spirit lamp 

 or gas flame, being sure not to 

 melt the paraffin. As the water 

 warms the paraffin expands and 

 stretches the sections out smooth. 

 A copper heating plate is good 

 (fig. 226), but an electric spreader 

 is best (fig. 22; 



FIGS. 228-229. ELECTRIC SPREADING 

 PLATE AND INFILTRATING OVEN. 



The projecting (About one eighth natural size. See also 



top enables one to heat this oven 



.,!_ i i i n T r A- The upper part of the oven with 



with a gas or alcohol flame. If an brass spread ^ g gt extending 8 cm. 



electric bulb is used, one of 30 to (Plate 38 cm. long, 18 cm. wide and 3 mm. 



40 watts is sufficient. All desired th L) Btii or tray for mfi i t rating dishes 



temperatures are possible byplac- (fig. 220). 

 ing the infiltrating dishes nearer 



or farther from the lamp ; and in % i Insulation where the cable passes 



j. r into the oven, 



spreading one can pass from a ow Hole to show when the curre nt is 



point over the lamp where the on, and for ventilation. 



rr i, ,v s Slide of serial sections spreading or 



paraffin may melt to the over- Drying 



hanging top which is only just 



warm. The dimensions of the oven giving optimum space and 

 the desired range of temperature are about as follows: Length 30 cm.; 

 width 1 8 cm.; height 12.5 cm. The brass spreading plate on top is 

 38 cm. long, 18 cm. wide and 3 mm. thick. The tray on the bottom 

 is about 2 cm. deep. The tray and oven are lined with asbestos. 



620. Drying the sections. After the sections are spread, drain 

 off most of the water, arrange the sections with a needle or scalpel, 



