I'llOTOMlCROGRAPIlY AS'D TFXIINICAI. MICROSCOPY 



113 



iiiouiitcd so that tlu->' lu.iy hv revolved. P"xtinction angles arc 

 read from a siiitahl>- graduated circle usually forming a part of 

 the anahzing eyepiece. 



l'Ki;r.\R.\IION OF SciXIMKNS 



Specimens, to be investigated or studieil by microscopic methods 

 nuist have a preparatory treatment in all cases except, perhaps, for 

 %ery lo\v-[Mnver work. Many samples recjuirc the preparation of 

 transparent sections: that is, a specimen of the object a few thou- 

 s.inilths of a millimeter in thickness so that it is transparent or at 

 least translucent; studies of woods, porcelains, papers, fibers, tissues, 

 insulating componnils, etc., are usually mailc with transparent sections. 



Fig. 12 — .-X sliding microtome for cutting microscopic sections. The work is held in 

 a clamp and a ver>' heav>' section razor, flat on one side and hollow ground on the 

 other is operated backward and forward on a slide rails. The return movement of 

 the razor operates the elevating mechanism to which the work is attached so that 

 the latter may l)e raised to cutting position hy predetermined increments. 



Hard specimens such as porcelain arc prepared by grinding, softer 

 materials such as wood sections are first prepared by suitable softening 

 processes and then are cut in an instrument called a microtome, a 

 form of which is shown in Fig. 12. 



Delicate structures require strengthening before they can be cut; 

 these are embedded in paraffin, cclloidin or glycerine gum. For 

 successful results gradual and thorough impregnation of the parts 

 is required and this operation may take several weeks. After the 



