Chapter II: General Statement of Methods 25 



Where desilicidation is necessary hydrofluoric acid may be em- 

 ployed, although, because of its property of attacking mucous 

 membranes, its use is attended with more or less danger for the 

 operator. It is added drop by drop to the tissue which has pre- 

 viously been placed in a paraffin-coated vessel (the acid attacks 

 glass). If the tissue is not too heavily impregnated with silica, 

 it is safer to use an old section razor and try to cut sections with- 

 out previously treating them with hydrofluoric acid. 



INJECTION METHODS 



The injection of colored masses into the blood vessels and 

 other vessels of the body is frequently practiced to aid in deter- 

 mining their distribution and their relation to the surrounding 

 tissues. The dye is termed the coloring mass and the substance 

 to which it is added, the vehicle. 



ISOLATION OF HISTOLOGICAL ELEMENTS 



Isolation is one of the most valuable means of forming a cor- 

 rect conception of cells and fibers. It has the advantage over 

 sections that the elements may be inspected in their entirety and 

 from all sides. The separation is accomplished, as already noted, 

 by (1) reagents which dissolve or soften cell cement and inter- 

 stitial material without seriously affecting the cells (maceration 

 or dissociation), or (2) mechanically by means of dissecting needles 

 (teasing), or both. Hardening and fixing reagents in general if 

 diluted to about one-tenth are efficient for dissociation. Gage 

 recommends normal saline as preferable to water for dilution. 

 The dissecting microscope or some kind of lens-holder and lens 

 are valuable aids in isolating tissue elements. For practical 

 methods consult chap, x ; for reagents, Appendix B, iv. 



NORMAL OR INDIFFERENT FLUIDS FOR EXAMINING FRESH TISSUES 



It is desirable frequently to examine fresh material in as near 

 a natural condition as possible, hence recourse is had to the so- 

 called indifferent fluids. While not wholly indifferent, they ordi- 

 narily produce but slight changes in tissues and their elements 

 from the view-point of the microscopist. The liquids most com- 

 monly used for this purpose are discussed in Appendix B, iii. 



