144 



THE ART OF MAKING MICROSCOPE SLIDES 



Infiltration 



Fig. 80. Tying paper collar round wood block. 





Fig. 81. Putting in first layer of celloidin. 



which a considerable quantity of calcium 

 sulfate or copper sulfate has been placed 

 as adehydrant. When the specimen is com- 

 pletely dehydrated, it is transferred to a 

 mixture of equal parts of absolute alcohol 

 and ether. The worker must remember 

 always to use anhydrous ether and not the 

 commercial variety. Specimens should re- 

 main in this mixture until they have been 

 completely impregnated. 



The actual process of getting the mate- 

 rial impregnated with 16% celloidin may 

 1)6 done in two ways. Either the ol)ject 

 may l)e i^laced in a considerable volume 

 of a dilute solution, and evaporated, or it 

 may be passed through solutions of in- 

 creasing strength. The writer prefers the 

 latter method since it is very difficult to 



evaporate an alcohol-ether mixture slowly 

 under dry conditions. Most people employ 



solutions of 2, 4, 8, and 



16% 



celloidin 



prepared bj- dilution of the 16% stock. 

 Every vessel used for dilution, as well as 

 the diluent itself, must be absolutely dry. 

 The object should be taken from the ab- 

 solute alcohol-ether mixture, and placed 

 in about 50 times its own volume of a 2 % 

 dilution in a glass-stoppered bottle, which 

 should in turn be kept in a sealed desicca- 

 tor while the imjiregnation is going on. 

 The time of impregnation naturall}' varies 

 according to both the size and the nature 

 of the object, but it is a rough and ready 

 rule for relative time that the material 

 should spend proportionately as long in 

 each solution as the concentration of the 



