THE CELLULOSE ACETATE METHOD 139 



tone. There they were left for two months, and excellent sections were ob- 

 tained. Further experiments showed that the passage through alcohols was 

 unnecessary. In the final experiments the pieces of wood were placed in water 

 and the air removed from them, after which they were put into pure acetone 

 for 1-2 hours and finally into the solution of cellulose acetate. It was found 

 that the length of time of immersion in the solution of cellulose acetate neces- 

 sary for softening the tissues varied with the hardness of the wood, the mini- 

 mum time for soft woods being two days; for woods such as oak and beech, 

 at least six days are required. Experiments were tried with sal {Shorea robusta) 

 and Pyingadu (Xylia dolabriformis) , one of the Indian ironwoods, which is 

 extremely hard. After fourteen days in the cellulose acetate solution it was 

 possible to obtain transverse sections of these hard woods. The cellulose 

 acetate solution is therefore capable of softening even the hardest wood in a 

 relatively short time. 



In order to stain sections — either hand or microtome — obtained by this 

 method, it is necessary to wash them in i)ure acetone for 1 to 2 minutes to 

 remove the cellulose acetate, wash in alcohol 1 to 2 minutes, and pass on to 

 the stains selected. Various staining methods for cell walls— such as aniUn 

 chloride, methjdene blue, and Congo red, ammoniacal fuchsin and Kleinen- 

 berg's haematoxylin, etc.— were tried with success. A comparison with 

 stained sections of untreated wood revealed no differences. DeHcate tissues 

 in the wood and hyphae of fungi infecting the wood also stain well and are 

 unaffected by the treatment. 



A satisfactory method of preparing sections of hard vegetable structures 

 is therefore supplied by the use of a 12 per cent solution of cellulose acetate 

 in pure acetone for softening and embedding.— H. S. Williamson, Imperial 

 College of Science and Technology. 



Correspondence with Mrs. Williamson indicates that the various 

 brands of cellulose acetate behave differently. Cellulose acetate ob- 

 tained from wood is unsatisfactory. We found that cellulose acetate 

 made from photographic films was also unsatisfactory. Mrs. William- 

 son used a cellulose acetate sold by Cellon (Richmond) Ltd., 22 Cork 

 Street, London, England, and manufactured by the Societe Chimique 

 des Usines du Rhone. The time may be shortened by keeping the 

 temperature at 40° C. 



In making the solution, use 12 g. of cellulose acetate to 100 c.c. 

 of pure acetone. 



