180 Methods of Observing Micro-organisms 



until ready to cut. The knife must be kept flooded with 

 alcohol while cutting. 



Celloidin is soluble in absolute alcohol, ether, and oil of 

 cloves, so that the staining of the sections must be accom- 

 plished without the use of these reagents if possible. 



Celloidin sections can be fastened to the slide, if desired, 

 by firmly pressing filter paper upon them and rubbing hard, 

 then allowing a little vapor of ether to run upon them. 



//. Paraffin. Pure paraffin having a melting-point of 

 about 55 C. is used. The hardened blocks of tissue are 

 passed through: 



Ninety-five per cent, alcohol, twelve to twenty-four 



hours ; 



Absolute alcohol, six to twelve hours; 

 Chloroform, benzole, or xylol, four hours; 

 A saturated solution of paraffin in one of the above 

 reagents, four to eight hours. 



The block is then placed in melted paraffin in an oven 

 or paraffin water-bath, at 5o-6o C., until the volatile 

 reagent is all evaporated, and the tissue impregnated with 

 paraffin (four to twelve hours), and finally embedded in 

 freshly melted paraffin in any convenient mold. In cutting, 

 the knife must be perfectly dry. 



The cut paraffin sections can be placed upon the surface 

 of slightly warmed water to flatten out the wrinkles, and 

 then floated upon a clean slide upon which a film of Meyer's 

 glycerin-albumen (equal parts of glycerin and white of egg 

 thoroughly beaten up and filtered, and preserved with a 

 crystal of thymol) has been spread. After drying, the slides 

 are placed in the paraffin oven for an hour at 60 C., so 

 that the albumen coagulates and fixes the sections to the 

 glass. 



When sections so spread and fixed upon the slide 

 are to be stained, the paraffin must first be dissolved in 

 chloroform, benzole, xylol, oil of turpentine, etc., which 

 in turn must be removed with 95 per cent, alcohol. The 

 further staining, by whatever method desired, is accom- 

 plished by dropping the reagents upon the slide. 



///. Glycerin-gelatin. As the penetration of the tissue 

 by celloidin is attended with deterioration in the staining 

 qualities of the tubercle bacillus, it has been recommended 



