150 Methods of Observing Micro-organisms 



Tissues preserved in 95 per cent, alcohol, Miiller's fluid, 4 per 

 cent, formaldehyd, and other ordinary solutions rarely show the 

 bacteria well. 



Embedding.— The ordinary methods of embedding suffice. The 

 simpler of these are as follows: 



I. Celloidin (Schering). — The solutions of celloidin are made in 

 equal parts of absolute alcohol and ether and should have the thick- 

 ness of oil or molasses. From the hardening reagent (if other than 

 absolute alcohol) pass the blocks of tissue through: 



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

 Absolute alcohol, six to twelve hours; 



Thin celloidin (consistence of oil), twelve to twenty-four hours; 

 Thick celloidin (consistence of molasses), six to twelve hours. 



Place upon a block of vulcanite or hard wood, allow the ether 

 to evaporate until the block can be overturned without dislodging 

 the specimen; then place in 80 per cent, alcohol 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 accomplished 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 

 S2°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 So°-ss°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 6o°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 

 accomplished by dropping the reagents upon the slide. 



