158 



THE ART OF MAKING MICROSCOPE SLIDES 



Refrigerants 



ally cut without having been infiltrated 

 with any material at all. The fact that this 

 procedure gives sections which may be 

 used for diagnostic purposes does not 

 mean that it should be used for any other 

 purpose. The sections so produced are of 

 bad quality compared with sections cut in 

 celloidin or paraffin; l^ut if the material is 

 first embedded in one of the media given 

 in Chapter 27 under the heading E 10, it is 

 possible to produce sections nearly as good 



which it is desired to obtain the best 

 possible section, and if time is of secondary 

 importance, the method of Clark 1947 

 gives sections that are very nearly the 

 equal of those which may be obtained by 

 the paraffin method. 



Choice of a Refrigerant 



Blocks are nowadays usuall}' frozen 

 with carbon dioxide from cylinders. The 

 cylinder is connectel through a needle 



Fig. 85. Applying Anderson's medium to tissue about to be frozen. 



as those obtained by the paraffin or nitro- 

 cellulose technic}ues. The choice between 

 the formulas there gi\-en should be based 

 on the length of time one is prepared to 

 spend on the preparation. If only a few 

 moments are available in excess of the ab- 

 solute minimum time required to cut with- 

 out embedding, better results will still be 

 obtained if the o]:)ject is smothered in 

 several layers of the solution of Anderson 

 1929. Much better results will be obtained, 

 however, if the specimen, after it has been 

 fixed in some material which will not alter 

 its chemical nature, is soaked in this 

 medium overnight in order to become im- 

 pregnated. In dealing with materials of 



valve to the object holder of the micro- 

 tome, so that a jet of supercooled carbon 

 dioxide may be projected against the 

 underside of the object. 



Other methods are available to those 

 who lack carbon-dioxide cylinders. The 

 standard method, prior to the introduc- 

 tion of carbon dioxide, was to replace the 

 tube leading from the carbon-dioxide cj-l- 

 inder with a tube entering a bottle con- 

 taining ether. Air was then blown through 

 the bottle by a tube, which dipped under 

 • the surface of the ether, so that the vapor 

 was projected onto the underside of the 

 block. The head absorbed by the evapora- 

 tion of the ether was very great and blocks 



