284 USE OF THE MICROSCOPE 



this it is only necessary to put a strip of filter paper in contact 

 with the edge of the coverglass opposite the drop of reagent, when 

 the water will run into the paper and the reagent will be drawn 

 under the coverglass by capillarity. This process is called 

 irrigation. It must be remembered, however, that very minute 

 objects such as starch grains are pretty certain to be swept along 

 in the currents, so that the slower process of diffusion should be 

 depended on wherever practicable. 



Some reagents should not be diluted with water at all. Such, 

 for instance, is chloroiodide of zinc. If a preparation already 

 mounted in water is to be treated with such reagents the cover- 

 glass should be removed and all of the water drawn off with filter 

 paper; then the reagent should be put on before the preparation 

 has time to become dry. If acid reagents are to be used especial 

 care must be taken not to allow them to get upon any parts of 

 the microscope; if this should happen they must be washed off 

 at once with plenty of water. The use of such acids as hydro- 

 chloric and sulphuric must be quickly over with, since their fumes 

 are injurious to the eyes as well as to the microscope. 



When through with the microscope see that it is clean in all 

 its parts and put it away under cover, where it will be free from 

 dust. 



