268 Modern Microscopy 



When it is desired to embed objects that have been in the 

 preserving fluid, they may be placed for a few days in a 

 considerable bulk of 50 per cent, alcohol, thence into 70 per 

 cent, alcohol, followed by 90 per cent, and absolute alcohol, 

 etc., completing the process of embedding exactly as if it was 

 following immediately after fixing. The practice of keeping 

 delicate structures intended for the microtome in strong 

 alcohol is to be greatly condemned, shrinkage and distor- 

 tion being usually inevitable. 



Another important step is the final enclosing of the in- 

 filtrated object within a cube of paraffin. There are 

 various ways of attaining this, but the very best and most 

 certain is that known as the watch-glass method, not, how- 

 ever, necessarily confined to the use of a watch-glass ; 

 indeed, the best utensil to use is the shallow, flat-bottomed 

 Berlin porcelain evaporating basin of the chemist, about 

 3 inches in diameter. Insist upon having a flat bottom. 

 The basin is well rubbed all over inside with a very little 

 glycerine, which is afterwards wiped away with a cloth, so 

 as not to leave any visible trace of the glycerine. The 

 basin is then placed upon the hot shelf of the retort stand 

 (p. 259) until it is a little warmer than the melting-point of 

 the paraffin used. Sufficient melted paraffin is then poured 

 in to well cover the object to be enclosed. The object or 

 objects four or five may be done simultaneously by this 

 method are then placed in the wax, which is still kept 

 fluid upon the hot shelf. By means of a hot needle arrange 

 the objects equidistant at about inch from the periphery 

 of the basin. Of course the contour of the subjects must 

 be known, and so arranged in the basin that the top 

 (that is, the part at which you wish to start the cutting) 

 is towards the bottom of the basin ; with a very long 

 object one of its sides should face the bottom of the basin, 

 and any method which readily suggests itself may be used 

 for noting its top and bottom for the intended cutting. It 

 may happen that your object will not readily stand ' top ' 

 downwards in the liquid paraffin, in which case place the 



