PRESERVING AND PREPARING PATHOLOGICAL SPECIMENS. 57 



organisms. A very small drop of this albumen mixture is placed on one 

 end of the slide, and with the ball of the finger or a fold of cloth, it is 

 spread over the rest of the slide in as thin a film as possible. While this 

 scarcely perceptible film of albumen fixative is still moist, the paraffin 

 sections or the ribbons of serial sections divided into proper lengths, are 

 laid upon the film and gently tapped down flat with a small camel's-hair 

 brush or the finger-tip. ' 



The slide with the attached paraffin sections is now heated over a 

 flame, warmed just sufficiently to begin to melt the paraffin ; this is a very 

 delicate point in the operation. Just enough heat must be used to melt 

 the paraffin and no more. If the slide be heated beyond this point, the 

 sections may be shrunken or completely ruined. While the slide is still 

 warm, it is plunged into a jar of xylol, oscillated to and fro a few sec- 

 onds, then placed in a jar of absolute alcohol, then passed through a 

 series of jars containing diifereut strengths of alcohol ninety-five per 

 cent, seventy per cent, fifty per cent, and thirty per cent, remaining a 

 few minute in each, and finally into water. Now the sections upon the 

 slide may be stained in whatever way desired, carried up through the 

 graded alcohols to absolute alcohol, then cleared in xylol or other clear- 

 ing media, and mounted in balsam. 



Tightly covered cylindrical jars the Coplin jar is excellent or wide- 

 mouthed bottles are used for the better manipulation of paraffin sections, 

 the whole slide being dropped into the receptacle for staining as well as 

 for the dehydration and clearing. 



SECTION CUTTING. 



This may be done in an emergency by the free hand with a razor 

 ground flat on the lower side, but better sections can be obtained by 

 means of a microtome, and practically all section cutting for microscop- 

 ical purposes is done by some form of this instrument. One of the 

 most useful of these is Thoma's. The Schanze microtome is also well 

 adapted for general work, as are some of the American instruments 

 made on the same plan. For cutting sections of tissues embedded in 

 paraffin, and especially for serial sections, the Minot microtome of the 

 improved form the Blake-Miuot microtome can, in skilled hands, cut 

 sections 1 // in thickness is excellent. 



1 Not infrequently very thin paraffin sections curl or become corrugated as the}' 

 leave the knife, so that it is difficult to place them flat upon the fixative film. Should 

 this occur, a few drops of water may be spread out in a thin layer over the albumen 

 film while it is still moist on the slide, and the whole slide, with the layer of water upon 

 its surface, is very gently heated over the flame just sufficiently to soften but not to 

 melt the paraffin. If the sections are then floated on the warm layer of water, they will 

 uncurl and flatten out. The water is then drained off, when the flattened sections will 

 lie flat upon the fixative film and remain fastened there. All traces of the water are 

 now allowed to evaporate in the air; or, the evaporation of the water may be hastened 

 by exposure to a temperature four or five degrees below the melting-point of the 

 paraffin. 



