T.S. Lily bud 



NITROCELLULOSE SECTIONS 



151 



topped off with the 16% solution and 

 placed in a closed vessel (a desiccator is 

 very convenient) in the bottom of which a 

 small quantit}' of chloroform has l)een 

 placed. After about a day it will be found 

 that the block has set to a rather opaque 

 jelly-like consistency and the whole thing 

 — block, wood, pins, and paper — -is then 

 thrown into a large container of anhydrous 

 chloroform. It should remain for a few 

 days in the chloroform and then be trans- 

 ferred to a considerable volume of 70% 

 alcohol, which is changed daily until no 

 smell of chloroform is observed. The block 

 — pins, paper, and all — may be kept in 

 70% alcohol until it is required. 



When it is decided to start sectioning, 

 the block is removed, the pins withdrawn 

 (a pair of phers will probably be neces- 

 sary), and the paper shaved from the sides 

 of the block with a sharp knife or razor. 

 It has been presumed in the directions 

 which have so far been given that the re- 

 quired sections will lie about one-third of 

 the distance from the base of the block, 

 since it is obvious that a block of this size 

 will not have the stability to permit cut- 

 ting at the top. Under these circumstances 

 the upper two-thirds of the block should 

 be removed, and it is safer to do this with 

 a fine saw than with a knife. If it is decided 

 that the portions of the upper block are 

 also required, the block may be cut with a 

 saw into as many pieces as are wanted, 

 , and each piece mounted on a celloicUn- 

 impregnated wooden block with the solu- 

 tion of Apathy given in Chapter 27 under 

 the heading E 22.1. Blocks mounted with 

 Apathy's cement are never as satisfactory, 

 however, as those which have been cast 

 directly onto a wooden block, as in the 

 first case. The reason for the retention of 

 the entire bud through embedding, is, of 

 course, to avoid disturbing the exceedingly 

 delicate relationships of the parts. This 

 would certainly ha^Dpen if one were to en- 

 deavor to embed one third of the bud 

 without leaving the remainder of it at- 

 tached for support. The lower third of the 

 block on its wooden holder is now mounted 

 in the object holder of a sUding microtome 

 and oriented roughly in the position de- 

 sired. The block will be found to be suffi- 

 ciently clear, after one has planed off the 



surface with a i-azor, to see down into it 

 and select that iM)int from which the de- 

 sired sections will be cut. No difficult}'' 

 will be e.xperienced in cutting these sec- 

 tions provided the knife slopes back away 

 from the block at an angle of about 30° 

 and hits the corner rather than the edge 

 of the block. Before cutting, provide a 

 beaker containing 70% alcohol, in which 

 the sections are to be accumulated, and 

 another beaker and brush containing 70% 

 alcohol, with which the knife blade and 

 the surface of the block are to be liberally 

 anointed while sectioning is in process. As 

 each section comes off, it should be re- 

 moved to the dish of 70% alcohol in which 

 the sections may be stored until they are 

 to be stained. It is excellent practice to 

 accumulate a large number of these sec- 

 tions and then to issue them to a class for 

 staining. Celloidin embedding is such a 

 prolonged process that it is difficult to use 

 in class periods, but there is nothing to 

 prevent blocks or sections from being 

 issued to classes to whom a detailed de- 

 scription of the manner in which they have 

 been prepared is given. 



A good combination for staining these 

 sections is Delafield's hematoxylin and saf- 

 ranin. However, the ordinary Delafield's 

 hematoxylin solution — the formula for 

 which is given in Chapter 20 as DS 11.122 

 Delafield (1885) — cannot be used at full 

 strength or it will be difficult to remove 

 from the celloidin matrix. It is better to 

 dilute the original solution \\dth about 10 

 times its own volume of a 1 % solution of 

 ammonium alum. One-tenth of 1 % hydro- 

 chloric acid in 70% alcohol and one of the 

 solutions of safranin given in Chapter 20 

 under the heading DS 11.42, are also re- 

 quired. The safranin should be either in 

 water or in an alcohol not stronger than 

 50%. The solution of Johansen 1940, for 

 example, contains enough Cellosolve to 

 soften a celloidin section undesirably. The 

 formula of Chamberlain 1915 is that com- 

 monly employed. 



Having accumulated these reagents in 

 three dishes, and a spare dish of 70% alco- 

 hol, the sections are placed in safranin. It 

 is difficult to overstain in this fluid and it 

 is probably most convenient to leave it 

 overnight. It should be left at least until 



