LABORATORY STUDIES AND DEMONSTRATIONS. 225 



the ribbon-method,* the knife being kept dry in either case. In 

 mounting they should be fixed by the collodion-method. (See 

 Collodion and Clove-oil.) 



B. Celloidin Method. This is especially applicable to deli- 

 cate vegetal tissues. After dehydrating the object thoroughly in 

 alcohol, soak it 24 hours in a mixture of equal parts of alcohol 

 and ether. Make a thick solution of celloidin in the same mix- 

 ture and soak the object for some hours in it. It may then be 

 imbedded as follows : Dip the smaller end of a tapering cork 

 in the celloidin solution, allow it to dry for a moment (blowing 

 on it if necessary), and then build upon it a mass of celloidin, 

 allowing it to dry a moment after each addition. Transfer the 

 object to the cork and cover it thoroughly with the celloidin. 

 Then float the cork in 82-85$ (0.842 sp. gr.) alcohol until the 

 mass has a firm consistency (24 h.). It may then be cut in the 

 microtome with the oblique knife, which must be kept dripping 

 with 82-85$ alcohol. Keep the sections in 82-85$ alcohol until 

 ready to mount them, then soak them for a minute in strong 

 alcohol, transfer to a slide, pour on chloroform until the alcohol 

 is removed, drain off the liquid, quickly add a drop of balsam, 

 and cover. (See also Whitman, 1. c., p. 113.) 



* See Whitman, 1. c. p. 71. 



