CHAPTER IX 



THE PARAFFIN METHOD 



For studies which demand very thin, smooth sections, the paraffin 

 method still holds the first place, with no near competitor. Some have 

 added to the paraffin a little of this or that or the other, and these 

 additions have corrected, somewhat, the imperfections of poor paraf- 

 fins. A thoroughly good paraffin will yield smooth ribbons at 1 ^ and, 

 in cold weather, ribbons f\ y. and even I n'm. thickness have been cut 

 in our laboratory. Modern microtomes, while rather comphcated, 

 give wonderful results and, to some extent, eliminate the element of 

 skill. The microtome, shown in Figure 20, with the cooling attach- 

 ment designed by Dr. Land, has cut even ribbons, Iju in thickness, 

 from the antheridial receptacles of Marchantia. With the compara- 

 tively inexpensive sliding microtome shown in Figure 2, page 9, 

 smooth, even ribbons of root-tips have been cut as thin as | m- It is 

 doubtful whether any other microtome, however expensive, has ever 

 cut thinner or smoother sections. Both of these microtomes were de- 

 signed by Mr, H. N. Ott, president of the Spencer Lens Company. 

 With these microtomes, especially with the small sliding one, serial 

 sections can be cut of pollen grains and spores too small to be seen by 

 the naked eye. 



Many of the principles involved in this method are general in their 

 application, and some of the processes are common to other methods. 

 One who has mastered the paraffin method should have little trouble 

 with any other method of preparing plant material for microscopic 

 examination. 



The following are the stages from fixing material to the finished 



mount : 



KILLING AND FIXING 



As stated in the chapter on "Reagents" (chap, ii), the purpose of 

 a kiUing agent is to bring the life-processes to a sudden termination, 

 while a fixing agent is used to fix the cells and their contents in as near- 

 ly the living condition as possible. The fixing consists in so hardening 

 the material that the various elements may retain their natural condi- 

 tion during all the processes which are to follow. Usually the same re- 



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