THE MICROSCOPE AND CELL-STRUCTURE. 67 



started or hastened by gently warming the slide. Similar movements 

 can be seen, even better, in the long cells of Stone worts (Nitella and 

 Chara), which grow in sluggish streams, and the cells forming the 

 hairs on the stamens of Tradescantia (often grown in greenhouses) 

 show more complicated protoplasmic movements. 



(d) A "moist-chamber slide" is very useful for observing circulation 

 of protoplasm in Elodea, etc. , also for watching the growth of pollen- 

 tubes. A ring of glass is cemented to a slide, and the Elodea-leaf, or 

 some pollen, is placed in a small drop on a cover-glass, which is then 

 inverted over the ring. A slide of this kind can be bought (Fig. 33, 1) 

 or can easily be made by using a ring of cardboard. 



1OO. Section Cutting. In examining the cellular structure of a 

 solid mass, e.g. a stem, root, or leaf, we can learn a certain amount by 

 crushing, teasing, or macerating the tissues, but the best results are 

 obtained by cutting thin sections in different directions. Fresh tissues 

 may be used for cutting, but it is often better to use "pickled" 

 material. The pickling fluid used for ordinary work is methylated 

 spirit diluted with about half its volume of water. Stems, roots, leaves, 

 etc., preserved in this way in glass jars are always ready for use. 

 Delicate plants, flowers, etc., may be preserved in 4 to 6 per cent, solu- 

 tion of formalin ; formalin as sold is a 40 per cent, solution. 



In taking a section, the tissue to be cut should be held between the 

 thumb and fingers of the left hand ; the razor in the right hand. The 

 tips of the four right fingers should rest on the back of the razor, and 

 the thumb in front, just behind the cutting edge. The cutting edge is 

 therefore directed inwards, towards the operator. The arms should be 

 brought up close to the body. Tissue and razor should both be wet 

 with alcohol. The blade of the razor may rest gently on the forefinger 

 of the left hand with the edge against the tissue. Then the razor is 

 drawn through the tissue with a sliding movement. With practice, 

 extremely thin sections may be cut. 



The sections should be removed from the razor by means of a brush, 

 and placed in a watch-glass containing alcohol or water. Several may 

 then be transferred to a slide and examined in water under the low 

 power, so that the best may be selected. By means of the linen rag 

 the excess of water may be removed, and iodine or other reagent added 

 according to the special points which the student wishes to determine. 

 The reagent should then be washed off with water, the excess of water 

 removed, a drop of glycerine added, and finally the cover-glass put on. 

 The section should always be mounted in the centre of the slide. 

 The cover-glass should be rested on its edge and let down gradually by 

 means of a needle. The section must not be allowed to get dry during 

 the process, or air-bubbles will make their appearance. If these do 

 appear, soaking the section for some time in alcohol will remove them. 

 The cover-glass must be perfectly clean and dry. 



Neatness and cleanliness are of great importance in practical work. 

 At first you will find that the sections are rather thick and often 

 obliquely cut. These are difficulties which can be got over only by 

 care and Dractice Do not attempt to draw a bad section . 



