IMBEDDING AND COOLING. 179 



This arrangement is very efficacious and very simple if the laboratory pos- 

 sesses a supply of water under sufficient pressure. 



In order to obtain the requisite vacuum without the aid of water under 

 pressure, a simple little apparatus has been designed by FRANCOTTE (Bull. 

 Soc. Belg. Micr., 1884, p. 45). In this the vacuum is produced by the con- 

 densation of steam. 



FOL (Lehrb., p. 121) employs the vacuum apparatus of Hoffmann, but 

 simplifies the arrangement for containing the paraffin. The paraffin is con- 

 tained in a stout test-tube furnished with a rubber stopper traversed by a 

 tube that puts it into communication with the pump. The lower end of the 

 test-tube dips into a water-bath. You pump out the air once or twice, wait 

 a few minutes to make sure that no more bubbles rise, then let the air in, 

 turn out the object with the paraffin (which by this time will have become 

 abnormally hard), and re-imbed in fresh paraffin. 



See also a paper by PEINGLE, in Journ. Path, and Bacterial., 1892, 

 p. 117 ; or Journ. Roy. Mic. Soc., 1892, p. 893. 



279. Imbedding and Cooling. As soon as the objects are 

 thoroughly saturated with paraffin they should be imbedded 

 by one of the methods given above ( 273). If the watch- 

 glass method be followed the paraffin-bath will naturally 

 have been given in the watch-glass used for imbedding, and 

 no special imbedding manipulation will be necessary. In any 

 case the important point now to be attended to is that the 

 paraffin be cooled as rapidly as possible. The object of this is 

 to prevent crystallisation of the paraffin, which may happen 

 if it be allowed to cool slowly, and to get as homogeneous a 

 mass as possible. 



Yery small objects may be taken out of the paraffin with a 

 needle or small spatula, and put to cool on a block of glass, 

 then imbedded in position for cutting on a cone of paraffin 

 by means of a heated needle in the manner described above 

 ( 273). In the use of the needle it should be noted that it 

 is important to melt as little paraffin as possible at one time, in 

 order that that which is melted may cool again as rapidly as 

 possible. 



If the watch-glass method be adopted, float the watch-glass 

 with the paraffin and objects on to cold water. Do not let it 

 sink till all the paraffin has solidified. When cool, cut out 

 blocks containing the objects ; do this with a slightly warmed 

 scalpel. 



If paper trays be taken, cool them on water, holding them 

 above the surface with only the bottom immersed until all the 

 paraffin has solidified, as if you let them go to the bottom at 



