CH. XI] PREPARATIONS BY THE PARAFFIN METHOD 



377 



days, depending on the size and character of the piece to be imbedded. 

 If the tissue was thoroughly dehydrated and well saturated with cedar 

 oil, the melted paraffin permeates the whole piece. 



612. Imbedding in paraffin wax. When the object is thoroughly 

 infiltrated imbed as follows: Make of strong writing paper a box 

 considerably larger than the piece to be imbedded. Nearly fill the 

 box with paraffin wax, place on a copper heater (fig. 226), and allow 

 to remain until bubbles appear 

 in it. Put the box on cold water 

 until a thin stratum of paraffin 

 solidifies on the bottom. Take the 

 piece of tissue from the infiltrat- 

 ing dish (fig. 220) and arrange in 

 the box for making sections in a 

 definite direction. Add hot para- 

 ffin, if necessary, and then place 

 the box on cold water. The more 

 rapid the cooling, the more homo- 

 geneous will be the block con- 

 taining the tissue to be cut. For 

 the best imbedding it is well to 

 drop 95% alcohol on the sur- 

 face as soon as a film has formed 

 in cooling. In warm climates 

 where cold water is not easy to 

 procure for cooling the blocks, 

 one may float the paper box on 

 95% alcohol arid with a pipette 

 (fig. 234) drop strong alcohol on 



FIG. 220. ELECTRIC INFILTRATING OVEN 

 WITH PROJECTING SPREADING PLATE. 



(About one eighth natural size. See 

 also fig. 228.) 



A Upper part of the oven with its 

 brass spreading plate projecting 8 cm. to 

 the left. 



B Base or tray holding the oven, and 

 the infiltrating and paraffin dishes, (i, 2, 



3, 4, 5, 6-) 



cr The electric cable and the porcelain 

 receptacle for the lamp bulb. 



The oven and tray are lined with as- 

 bestos, but there is none under the spread- 

 ing plate. The dimensions are : Brass top, 

 38 x 1 8 cm., 3 mm. thick. 



Oven, 30 cm. long, 18 cm. wide, 12.5 cm. 

 high. Tray, 30 x 18 x 2 cm. 



the sides of the box and on the top of the paraffin as soon as a sur- 

 face film has formed. 



It is very desirable to mark on the box the name of the imbedded 

 object and to indicate which end or face is to be cut (see also 657). 



613. Fastening the block to a holder. Use one of the block 

 holders or object discs furnished with the microtome, or a short 

 stove bolt (fig. 222). Heat the larger end and press the paraffin 

 block against the hot metal until it melts the paraffin Hold the two 

 together while cold water flows over them. When cold the block 

 is firmly cemented to the holder. Pains should be taken to have the 

 axis of the block parallel with the long axis of the holder; and one 



