CHOICE AND USE OF APPARATUS 



the solution to flow on to the upper surface of the 

 slip. Now, one of the pieces of blotting paper must 

 be placed upon the opposite side of the slide so that 

 it will stand up ; it must then be moved till it just 

 touches the edge of the cover slip. The blotting 

 paper will absorb the water from beneath the cover 

 slip, and in doing so the iodine solution will be drawn 

 along to take the place of the water. By proceeding 

 in this manner and replacing the blotting paper with 

 a new piece as it becomes moist, also replenishing the 

 drop of iodine as it is used up, we act upon our object 

 with a stronger and stronger solution, and, in 

 Spirogyra, the object which we took as our example, 

 we can see beautiful rosettes of starch grains, 

 arranged at regular intervals along the green bands 

 of chlorophyll. This method of staining may be used 

 in most cases where we merely require a temporary 

 stain; by reversing the process and drawing water 

 over the object by means of blotting paper, it may 

 be used in washing sections and parts of plants. For 

 very small objects, such as starch grains separated 

 from the plants in which they are formed, the method 

 is hardly suitable, for they are liable to be drawn 

 along in the stream of liquid and lost. 



For more permanent staining processes, we must 

 use our watch glasses, into which we pour the various 

 liquids necessary for the operation. The precise 

 methods of staining, the periods during which objects 

 should remain in the staining solution, and the chemi- 

 cals used for removing excessive stain vary, as may 

 be guessed, according to circumstances. Some 



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