CHOICE AND USE OF APPARATUS 



desirous of examining ; in other cases it is necessary 

 to stain when we wish to know the nature of the 

 various parts of our object. Suppose, for example, 

 we wish to find out whether a plant section contains 

 starch, we then add iodine solution, and if any parts 

 stain deep blue we know at once that starch is 

 present. There are other stains for other plant and 

 animal substances; stains for woody matter, stains 

 for fats, &c., but the art of staining is a science in 

 itself, and would require many chapters to describe 

 fully. Most of the objects described in this book 

 can be studied in the natural state, but, even so, they 

 may be rendered far more beautiful by staining. 



The method we described for the staining of 

 bacteria does not apply to such objects as plant sec- 

 tions, &c., and we propose to describe, as briefly as 

 possible, how to proceed with such objects. Suppose 

 we are examining one of the common pond plants, 

 Spirogyra for instance, and we wish to see whether 

 it contains starch. Our specimen is in a slide, in a 

 drop of water, and covered by a cover slip. In the 

 first place, we must obtain some fiuffless blotting 

 paper — the ordinary filter papers sold by all chemists 

 are excellent — from it we must cut about half a dozen 

 pieces, about half an inch by one inch, the exact size 

 is not important, and they need not be measured. 

 These we must fold in the centre, so that they can 

 be made to stand up like an inverted V. From our 

 bottle of iodine solution we take a drop of the liquid 

 on the end of a glass rod and place it carefully at 

 one edge of the cover slip, avoiding allowing any of 



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