OF MICROSCOPIC OBJECTS. 



into the pith, and when this is dry thin sections could be 

 cut and the gum washed out again, and these could be 

 mounted in balsam. 



The plan adopted by most practical histologists for cut- 

 ting sections of soft tissues is as follows : The tissue to be 

 cut is first hardened by immersion in a chromic acid solu- 

 tion varying in strength from 0'25 to 2 per cent., or by im- 

 mersion in alcohol. The substance to be cut may then be 

 embedded in melted wax and spermaceti, in proportions 

 suitable to the nature of the substance to be cut ; when 

 this is cold the section may be cut with a razor ground 

 flat on one side, and may then be floated off in spirits of 

 wine. 



These sections mount very well in Canada balsam, if 

 after being removed from the spirit they are immersed in 

 oil of cloves till they become clear, then put into turpentine 

 before the balsam. The thinness of the section will depend 

 very much on the dexterity of the operator, but section- 

 cutting instruments for soft tissues can now be obtained at 

 most scientific instrument shops. 



When sections of softer substances are required, no instru- 

 ment can be compared with " Valentin's knife," which con- 

 sists of two steel blades lying parallel with each other and 

 attached at the lower end. The distance of separation may 

 be regulated at will by a small screw near the handle. 

 When, therefore, a section is wanted, the substance must 

 be cut through, and betwixt the blades a thin strip will be 

 found, which may be made of any thickness, according to 

 the distance of their separation. By loosening the screw 

 the blades may be extended, and the section may be floated 

 out in water if the damp will not injure it. The knife cuts 

 much better if dipped in water or glycerine immediately be- 

 fore use, and also when the substance to be operated upon 

 is wet, or even under water altogether; but care must be 

 taken, after use, to clean the blades thoroughly and oil them 

 before laying by, if the place is at all damp. This instru- 

 ment is most useful in such subiects as anatomical prepara- 



