APPARATUS 



11 



put on during sharpening, thus getting a proper bevel. Modern razors, 

 ground hollow on both sides, are worthless for histological work. 



There should be two good hones: a fine carborundum hone for the 

 prehminary sharpening, and a yellow Belgian hone for finishing. 

 About 10X2| inches is a good size. If the second hone be quite hard 

 and the finishing skilfully done, little or no stropping may be neces- 

 sary. The best strops used by barbers are satisfactory for microtome 

 knives. 



Fig. 7. — Land's electric constant apparatus, showing diagram of the automatic switch, as de- 

 scribed in the Botanical Gazette of November, 1911. 



Great improvements have been made in paraffin baths. A type de- 

 vised by Dr. Land has never been surpassed in accuracy. The novice 

 is likely to have trouble with it. This bath is not on the market, but, 

 with the help of the diagrams, one can make it and having made it 

 one can use it (Figs. 7 and 8). A detailed description of the thermostat 

 and heater is given in the Botanical Gazette of November, 1911. Unless 

 the coil in the heater is perfectly protected, there will be a short cir- 

 cuit; but this danger can be obviated, in large measure, by using oil 

 instead of water in the jacket. 



Another form of heater, using long electric bulbs instead of a coil, 

 can be made with less skill. From a sheet of transite | inch thick, 

 make a box just the size of the bottom of the bath and about 4 inches 



