34 



BO TA NIC A L MICRO TECHNIQ UE. 



FIG. 16. Paraffine oven. 



For a paraffine oven I use in Tubingen with the best results 

 an ordinary double - walled drying- 

 oven (cf. Fig. 1 6) with the mantle 

 filled with liquid paraffine, into which 

 projects a Desaga thermostat. This 

 is so arranged that the temperature 

 of the fluid paraffine is about 63 C.* 



48. Finally, to enclose the object 

 quite saturated with paraffine in a 

 block of paraffine suitable for cutting, 

 it is convenient to place a drop of 

 glycerine in a watch-glass of about 

 60 mm. diameter and to rub it over 

 the inner surface of the glass until the 

 glycerine can no longer be seen.f 



The watch-glass is then somewhat warmed and filled 

 with melted paraffine. When this has cooled to near its 

 melting-point, which may be known by its hardening at the 

 edges when lightly blown upon, the objects to be enclosed 

 are placed in it and so oriented with a heated needle that 

 suitable blocks of paraffine can be cut from the mass when 

 cool. 



In order to prevent crystallization in the cooling paraffine 

 so far as may be, it should be cooled as rapidly as possible. 

 This is best accomplished by placing the watch-glass, as 

 soon as the objects are oriented, upon a large vessel of cold 

 water, where it will readily float if carefully placed upon 

 the surface. For the same reason it is desirable to place 

 the objects near the edge of the watch-glass where the par- 

 affine is thinnest. When the paraffine is quite cold it sepa- 

 rates easily from the watch-glass and is then cut into rect- 

 angular blocks two or three centimetres long, each of which 



* The so-called " Naples water-bath " recommended by Paul Mayer (I) is 

 also very convenient. [This bath in various more or less modified forms 

 may be obtained of American dealers and in its best forms is very useful in 

 the work of imbedding and mounting.] 



f This serves the purpose of aiding the subsequent separation of the paraf- 

 fine from the watch-glass. 



