CELL SHAPE 



57 



CELLOIDIN IMBEDDING 



Nature adheres to the same three-rayed 

 intersection and molds the cells in that 

 shape which provides the smallest sur- 

 face area for closely crowded bodies. 

 Lewis found that this could be deter- 

 mined mathematically as a 14-sided 

 figure and by careful reconstruction of 

 actual cells proved that they were all 

 primarily tetrakaidecahedral in shape. 

 Examination of his clear illustrations 

 will be more helpful than pages of de- 

 scription. The same architectural prin- 

 ciples apply to many other cell 

 aggregates, like fatty tissue for ex- 

 ample. No longer is the histologist 

 justified in vaguely referring to such 

 cells as polyhedral. Evidently in the 

 construction of epithelial surfaces the 

 cells are fitted together in a much more 

 effective way than bricks in the building 

 of a wall. Except for the reference, 

 the above paragraph is quoted from the 

 Second Edition of Cowdry's Histology, 

 Philadelphia: Lea & Febiger, 1938. 

 Celloidin Imbedding. Celloidin is a kind 

 of generic term covering various cellu- 

 lose compounds, nitrocellulose, soluble 

 gun cotton, etc., employed for imbed- 

 ding. The collodions are solutions of 

 pyroxylin made as specified in the 

 U.S.P. Pyroxylin U.S.P. XI consists 

 chiefly of cellulose tetranitrite (Merck 

 Index, p. 465). Obviously a purified, 

 nonexplosive form of pyroxylin is 

 necessary. There are several in the 

 market of which Parlodion (Mallinck- 

 rodt) is the one used in our laboratory. 

 The Bensleys (p. 37) use as celloidin 

 "RS 5 sec. low viscosity nitrocellulose 

 30 per cent solvent in absolute alcohol'- 

 obtained from the Hercules Powder Co., 

 Gillespie, N. J. To make 20% stock 

 solution they dissolve 140 gms. nitro- 

 cellulose in 250 cc. ether and 210 cc. 

 absolute alcohol. This requires 4-5 

 days shaking occasionally. It is diluted 

 with ether alcohol to make 10 and 5% 

 solutions respectively. Nitrocellulose 

 is much used especially in neurological 

 technique. It is abbreviated L.V.N. 

 Some advantages over "celloidin" are 

 claimed for it by Davenport, H. A., 

 and Swank, R. L., Stain Techn., 1934, 

 9, 137-139. 



Celloidin imbedding is less popular 

 than it used to be owing to certain 

 advantages of Paraffin Imbedding rein- 

 forced by the mania for speed. But 

 celloidin imbedding is in some respects 

 superior. It yields sections in which 

 the affinity of the tissue components for 

 dyes is often greater. Clearing of the 

 tissue in xylol and similar fluids is not 

 required and it need not be subjected to 

 heat. The tissue usually shrinks less 

 and seldom becomes so brittle. Brain 

 specimens can easily be cut in celloidin 



even after long mordanting. When 

 sections are required of large pieces of 

 tissue in which cavities, such as the 

 lumina of the paranasal sinuses, alter- 

 nate with stout bony walls this method 

 is indicated because the celloidin in the 

 spaces gives more support than paraffin 

 (see also Double Imbedding). 



The slow method, which is the best, 

 requires for tissue slices not more than 

 5 mm. thick, at least 1 day each in 95% 

 alcohol, absolute alcohol, and in half 

 absolute and ether. This is followed by 

 1 day in thin celloidin (about 4% dried 

 strips of celloidin — Parlodion, Mal- 

 linckrodt — dissolved in equal parts 

 absolute alcohol and ether) and 1 or 

 more weeks in thick 8% celloidin. 

 The tissue, with some celloidin about it, 

 is then mounted on a fiber block, hard- 

 ened in chloroform 1-2 hrs. and stored 

 in 80% alcohol. 



Mallory (p. 60) gives the following as 

 a rapid method. Fix thin tissue pieces 

 12-18 hrs. in Formalin-Alcohol. Then 

 95% alcohol, 2 changes, 2 hrs. ; absolute 

 alcohol, 2 changes, 3 hrs. ; alcohol-ether, 

 3 hrs. ; thick celloidin 12-15 hrs. ; mount 

 and harden in chloroform, 1 hr.; 80% 

 alcohol. 



A still quicker technique has been 

 proposed (Richardson, G. D., J. Tech. 

 Meth., 1934, 13, 81) : To make celloidin 

 solution, add 1100 cc. absolute ethyl 

 alcohol to 8 oz. celloidin (dried in air) 

 and leave over night. Add 1100 cc. 

 ether. Let stand several days. It is 

 ready when celloidin is dissolved. 

 Fix tissue in 10% formalin, 2 hrs.; 

 acetone, 2 hrs. ; oil of cloves ^-2 hrs. or 

 until clear; celloidin 6 hrs. at room 

 temperature or ^3 hrs. in water bath 

 at 55 °C. (being careful to keep away 

 from flame). Block and harden in 

 chloroform ^2 hrs. 



Another so called hot celloidin method 

 is proposed with all steps in the tech- 

 nique at an elevated temperature 

 (Koneff, A. A., and Lyons, W. R., Stain 

 Techn., 1937, 12, 57-59). Fix pieces 

 not thicker than 2-3 mm. in 10% neutral 

 formol, Bouin or Susa. Wash in aq. 

 dest. several changes (1 hr. each) at 

 room temperature. Dehydrate at 50 °C. 

 70, 80, 95 and abs. ale. 2 changes J hr. 

 each. Equal parts abs. ale. and ether 

 1 hr. Infiltrate at 56°C. in (1) 10% 

 nitrocellulose (R.S. ^ second, viscosity 

 A"~25> Hercules Powder Co.) in equal 

 parts abs. ale. and ether, 1 hr. (2) 25% 

 in 45 cc. ale. -f 55 cc. ether, over night. 

 (3) 50% in 40 cc. ale. + 60 cc. ether 

 2-3 hrs. Then transfer tissue to micro- 

 tome block moistened with ether-alcohol. 

 Add 50% nitro-cellulose and the tissue. 

 Harden in 2 changes chloroform during 

 1 hr. Then pass through 3 changes 80% 



