84 HOW TO WORK 



this way excessively thin sections of hair in great numbers may be 

 obtained, and can be easily removed from the lather, well washed 

 in distilled water and dried at the ordinary temperature. 



156. On cutting Sections of Wood and Textures of that Character. 



-Thin sections of various woods and other vegetable textures 

 of a certain degree of firmness may be cut with the aid of the 

 instrument represented in pi. XXI, fig. 137. A piece of wood, after 

 having been allowed to soak for some time in water, is placed in 

 the hole, and kept in its position by the side screw. Upon turning 

 the lower screw the wood is forced above the brass plate. A clean 

 section is now made with a sharp strong knife or razor. By turning 

 the screw beneath, very slightly, the wood is forced above the surface 

 of the brass plate, and thus a section of any required thickness 

 may be obtained. 



ON THE SEPARATION OF DEPOSITS FROM FLUIDS. 



Before we can ascertain the nature of a deposit suspended in a 

 fluid, it is necessary to separate it as much as possible, and 

 collect it into a small space. Diffused as the deposit often is 

 through a large bulk of fluid, the observer would scarcely be sur- 

 prised if he failed to distinguish it, when a drop was placed under 

 the microscope. 



The ordinary method of separating deposits from fluids is by 

 filtration. The arrangement of the funnel and the mode of fold- 

 ing the paper, for filtering, are shown in pi. XXII, figs. 139 and 

 147. Filtration, however, will not answer for microscopical purposes, 

 when a mere trace of deposit has to be collected from a large quantity 

 of fluid. Moreover, particles from the filtering paper often become 

 mixed with the deposit and lead to confusion. Hence other modes 

 of proceeding must be resorted to. 



157. Conical Glasses. In order to collect the deposit for micro- 

 scopical examination, the fluid containing it is placed in' a conical 

 glass, the lower portion of which is narrow, not, however, termi- 

 nating in a point but in a slightly rounded extremity. After 

 standing for some hours, the deposit falls to the narrow portion 

 of the glass, and may be removed with the pipette. A useful form 

 of conical glass is represented in pi. XXII, fig. 141. 



158. The Pipette consists of a glass tube, about ten inches in 

 length, the upper extremity being slightly enlarged, so that the finger 

 may be conveniently applied to it, and the lower orifice contracted, 

 so as to be about one tenth of an inch in diameter. It is convenient 



