ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



569 



have not been embedded. The instrument used is Reichert's sliding 

 microtome. For hard objects a wedge-shaped knife, for soft objects a 

 hollow-groimd razor is used. The knife and the object to be cut are 

 kept moist with alcohol, glycerin, or water. Pieces of hard wood are 

 boiled in water or soaked in glycerin-alcohol before cutting. Leaves are 

 fixed in elder-pith or cork. The method is specially suitable for pre- 

 paring sections of roots, barks, and seeds. 



Constant Temperature Oven for ParaflBn Embedding.* — This appar- 

 atus, devised by G. Y. Rusk (fig. lob) consists of a box constructed of 

 sheet copper tinned on the inside, the dimensions of A being 17 X 15 

 X 12 in. In front are two sunk chambers 6^ X llf X lOj in. (D and 

 E). On the inner walls of these are projections for shelves or for trays 



Pig. 105. 



containing paraffin. D represents a closed door which is omitted on the 

 other side to show the internal arrangements. Into the space between 

 the outside wall and the sunken cliambers, acetone is poured through 

 the opening just below A. This opening is provided with a reflux con- 

 . denser : one of the Soxhlet type answers well. Into the chambers D and 

 E are openings for thermometers. Near the base of the side B is a 

 cylinder F, designed to contain the heating electric cartridge. C is a 

 cross-section of the door showing details of construction. When the 

 apparatus is to be set up, a layer of asbestos is applied to prevent heat 

 loss. It takes about an hour to heat the apparatus up to 56" C, and 

 above this point it cannot go as long as acetone is present. The amount 

 of acetone used need only be as much as will cover the heating unit. 

 The electric cartridge is like those used in flat-irons. 



* Zeitschr. wiss. Mikrosk., xxix. (1912) pp. 85-6 (1 fig.). 

 October IGth, 1912 2 q 



