302 CHAPTER VIH. 



132. Imbedding and Cooling, As soon as the objects are 

 thoroughly saturated with paraffin they should be imbedded 

 by one of the methods given above ( 126). 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 

 ( 126). 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. 



For BOVEEI'S plan for imbedding numerous very small objects see " Em- 

 bryological Methods," and for that of LATJTEBBORN see '" Protozoa." 



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 OQ 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 once you will probably get cavities filled with water formed 

 in your paraffin. Or you may put them to cool on a block 

 of cold metal or stone. 



Preparations imbedded in the metal " squares " are cooled 

 in a similar manner. 



SELENKA cools the mass by passing a stream of cold water through the 

 imbedding tube described above ( 126). MAYER cools the mass in the 

 paraffin-tight moulds 126 by passing cold water through a special movable 

 water-bath, which allows of the arrangement of the objects by transmitted 

 light under a dissecting microscope, see Mitth. Zool. Stat. Neapel, iv, 1883, 

 p. 429; Intern. Munaisscltr. Anat. Hist., iv, 1887, p. 39. 



