CHAPTER XI 



THE CELLULOSE ACETATE METHOD 



When the celkilose acetate method first appeared, more than ten 

 years ago, we hoped that it was destined to be as successful with hard 

 woody tissues as the Venetian turpentine method has been with uni- 

 cellular and filamentous forms; but, up to date, American investiga- 

 tors have found nothing to arouse any enthusiasm for this method, 

 which seems to be at its best in the fogs of London. We have obtained 

 the cellulose acetate from Cellon and tried it repeatedly with hard and 

 soft woods, but have never secured sections which could be compared 

 with those obtained by other methods. However, no one but the 

 authors got good results with Venetian turpentine for many years 

 after the method was published; so, let us hope that the method will 

 yet yield as good sections on this side of the Atlantic as it does on the 

 other. 



Hard woods like oak, and even harder material, have yielded 

 smooth thin sections. Cellulose acetate does not injure the finer de- 

 tails of structures and, on that account, is superior to hydrofluoric 

 acid. We are quoting, in full, Mrs. Williamson's account in the Annals 

 of Botany for January, 1921. 



A NEW METHOD OF PREPARING SECTIONS OF HARD 

 VEGETABLE STRUCTURES 



In order to prepare sections of hard vegetable structures it is essential that 

 some method should be devised by which the structure is not only embedded 

 but softened, so that sections can be cut easily and smoothly. After various 

 methods had been tried, the cellulose acetate method successfully used by 

 Dr. Kernot for embedding and sectioning the fabric of aeroplane wings was 

 used. It was discovered that this method not only embedded hard vegetable 

 structures, but also softened them so that sections are easily obtained. It 

 proved best to use cellulose acetate of French manufacture made from pure 

 cellulose, as the viscosity is more uniform than that of English manufacture, 

 which is obtained from the cellulose of wood. 



In the preliminary experiments pieces of oak and beech, cut into half-inch 

 cubes, were passed through strengths of alcohol, then placed in pure acetone 

 for two hours and finally into a 12 per cent solution of cellulose acetate in ace- 



138 



