446 XXXII. CELL-DIVISION AND NUCLEAR DIVISION. 



is a small perforated vessel of unglazed porcelain, in which the 

 object can remain while the fixing fluids act by means of the 

 perforations. 



Out of the 96 per cent, alcohol the objects must be laid for an 

 hour or two in absolute alcohol, and care must be taken that this 

 alcohol is to all intents and purposes free of water. This can be 

 best secured by adding to commercial absolute alcohol some sul- 

 phate of copper which has been thoroughly dehydrated anew by 

 calcining. The object is thence transferred to a mixture of half 

 absolute alcohol, half chloroform, in which it will at first float, 

 but must ultimately sink. In some cases this may take a fairly 

 long time, but then, and not till then, we may transfer it to pure 

 chloroform. After complete saturation in this, that is for pieces 

 of tissue in not less than twenty-four hours, the object is placed in 

 a glass box or a porcelain basin with chloroform to which a little 

 paraffin of melting-point 45 C. has been added. This vessel is 

 placed in a warm chamber, paraffin oven or water bath, heated to 

 about 55 C., and left there for one or two days, or, if the object 

 is not very permeable, for even longer. From this solution the 

 object is placed in pure melted paraffin of 45 C. melting-point, 

 remaining therein in a warm chamber for about a day, then trans- 

 ferred to paraffin of 52 C. melting-point for one or two days in 

 all cases long enough to be completely saturated. The fluid 

 paraffin and the object are now turned into a sufficiently small 

 vessel, for example, a small "box" or trough made of folded 

 writing-paper, or a watch-glass which has been previously smeared 

 with glycerine. An attempt is made to place the object in the 

 most suitable position, or, if there are a number, to distribute 

 them in the paraffin, and this is then rapidly solidified. This can 

 be effected by plunging the small vessel into cold water. If watch- 

 glasses are used for the purpose, they should first be floated on 

 the cold water, and only immersed when the surface of the paraffin 

 has set. Smearing the watch-glass with glycerine enables the 

 hardened paraffin to be easily separated from it. We then cut the 

 paraffin into small cubes or rectangular prisms. It is desirable 

 always to keep paraffin of 52 C. melting-point in a glass beaker 

 in the warm chamber, and thus at all times to have it fluid for use ; 

 and one can then use just so much as is necessary to produce a 

 proper distribution of the objects in the watch-glass. A watch-glass 

 can even be filled with such paraffin, and the objects taken singly out 

 of the paraffin in which they were impregnated, and at once suit- 



