1 88 PRACTICAL MICROSCOPY. 



five parts of paraffin with one part of hog's lard. Both of 

 these mixtures are liable to become loose in the cylinder, 

 often rotating during the cutting operation, and also 

 " rising," and thereby spoiling the work by uneven 

 thickness. 



Mr. John Barrow has improved this bedding by making 

 a mixture of naphthalin and stearine in certain proportions, 

 which vary according to the temperature of the air and 

 its consequent behaviour under the knife. It can be mixed 

 in quantity and kept in a large glue-pot, or even a stone- 

 ware jar or preserve-pot, and remelted by standing in hot 

 water when required for use. 



This mixture does not become loose in the well of the 

 microtome like the paraffin mixture, and never " rises," so 

 that sections are easily cut of a uniform thickness. 



Having soaked the stem in water, in order to soften it 

 somewhat, it should be dried externally and dipped into 

 the following solution, which has been carefully filtered : 



Finest gum-arabic . . . . 60 grains. 



Glycerine 5 drops. 



Alcohol I o drops. 



Water 2 ounces. 



The stem must then be withdrawn and allowed to drain 

 upon blotting-paper until surface dry, when it is held in 

 the fluid bedding agent in the well of the microtome, until 

 the naphthalin mixture has become hard, the plug having 

 been previously depressed, by means of the screw, to the 

 depth required. 



When quite cold the cutting may be commenced, and 

 the first cut or two made with an ordinary razor and dis- 

 carded, being only intended to level down and to ascertain 

 if all be right. After levelling, the second cut with the 

 section razor should be examined under a low power, and 

 if it is not thin enough more care must be taken with the 



