156 METHODS OF MICROSCOPICAL RESEARCH. 



and if necessary, wash it on the slip in the moisture 

 from the breath, which moisture will also cause the 

 diatom to adhere to the bristle ; now draw down 

 the sliding frame and place the diatom on the cover. 

 In this way any number of diatoms, &c., may be 

 transferred from the lower slip to the thin cover 

 and arranged as desired, and when the moisture 

 from the breath has evaporated, it will be found 

 that the forms are firmly affixed to the cover, whilst 

 the glass roof over the " mount " has preserved it 

 from all danger or dust during its preparation. 

 The cement with which the diatoms are to be 

 affixed to the thin cover is made thus : In 1 

 ounce of distilled water dissolve 2 grains of best 

 gum arabic, without heat. When the gum is dis- 

 solved add 3 minims of glacial acetic acid, to pre- 

 vent fungoid growth, and the least trace of sugar 

 to prevent the solution from cracking as it dries. 1 

 The solution should be carefully filtered through 

 the finest filter paper, and the filtering repeated at 

 intervals of a few weeks. 



For years experiments were in progress in the 

 hope of discovering a medium in which to mount 

 diatoms, which should be more satisfactory, in 

 respect of its refractive index, than Canada balsam, 

 and equally reliable and permanent ; many such 

 media have been tried phosphorus, balsam of 

 tolu, oil of cloves, and others ; but it is unneces- 

 sary to enter into details concerning them, since the 



1 For affixing delicate insect dissections to the slip or cover, 

 this cement should be made with 8 grains of gum arabic 

 to the ounce of distilled water, and for polycystina or forami- 

 nifera with 10 grains, and ior sponge spiculae with 6 grains to 

 the ounce. 



