Production of Sections 273 



pure xylol. The various fluids will work a long time with- 

 out changing ; the only thing necessary in transferring 

 objects from one fluid to the next is to lift out the tube 

 containing the objects, drain for a moment, and place in 

 the next bottle. After the pure xylol-bath, the empty 

 tube is placed upon the top of the oven to evaporate the 

 xylol, and returned to one of the alcohol bottles ready for 

 the next objects. The best vessels for infiltrating small 

 objects in the oven are the small staining cells sold by 

 opticians, consisting of a solid cube of glass with a con- 

 cavity excavated upon its upper surface. The advantage 

 of these cells is that, being thick, they retain the heat well, 

 and the paraffin does not begin to cool directly they are 

 removed from the oven for examination. They never upset 

 in the oven, and they are readily cleaned. 



Melting Points of Paraffin. — The paraffin for embed- 

 ding should be kept in a Berlin porcelain evaporating basin 

 with handle, spout, and lid, and should be placed in the oven 

 a couple of hours before required for embedding. Never melt 

 your embedding paraffin over a Bunsen or spirit lamp, as the 

 result may be a superheated paraffin, a consequence of which 

 is a harder paraffin than you had at first. A considerable 

 amount of misconception exists as to the best kind of paraffin 

 to use — that is to say, the best melting-point. All grades, 

 however, ai^e useful, it only being necessary to make an ad- 

 justment in the temperature of the laboratory to suit the 

 thickness of the sections required. If your room is at 15° C, 

 and you require sections 10 fj- thick, paraffin melting at 45° C. 

 will fulfil your requirements ; but for sections 5 /a thick, 

 with the same room temperature of 15° C, you will require 

 a harder paraffin — say, 48° C. or 50° C. ; and for sections 

 1 /It thick and the same room temperature the wax must 

 have a still higher melting-point. If, on the other hand, 

 you wish to cut sections 30 f* thick at the same room 

 temperature of 15° C, then the melting-point of the wax 

 should be lower — say, 42° C. — or you may raise or lower 

 the temperature of the room to suit the melting-point of 



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