132 Modern Microscopy 



LESSON I. 



HARDENING AND PRESERVING ANIMAL 

 TISSUES AND ORGANS FOR MICRO- 

 SCOPICAL EXAMINATIONS. 



Fresh untreated tissues are unsuited for microscopical 

 purposes, but it is sometimes advisable to observe the 

 appearance of some specimens, such as muscle-fibres, 

 tendon, connective tissues, and nerve-fibres, while fresh. 

 When this is desired, the tissue must be examined in 

 certain fluids called normal fluids that will alter its character 

 as little as possible. Those generally used are : (1) blood 

 serum ; (2-) the aqueous humour from a fresh eye ; and 

 (3) normal or f per cent, salt solution. The two former 

 are difficult to obtain, but the latter can be made at any 

 time, and it will answer for most purposes. Place a small 

 piece of the tissue on a slide, add a drop or two of salt 

 solution, take two needles fixed in holders and carefully 

 separate the fibres from each other ; this process is called 

 teasing. When sufficiently teased, apply a cover- glass and 

 examine. You may now wish to irrigate with some staining 

 reagent ; if so, place a few drops of the stain at one edge of 

 the cover-glass, and apply a piece of blotting-paper to the 

 other side ; this will absorb the salt solution, and the 

 staining fluid will follow and take its place around the 

 tissue ; the slide may then be placed under the microscope, 

 and the action of the reagent observed. 



These specimens cannot, as a rule, be kept. For perma- 

 nent preparations the tissues or organs must be hardened. 

 This is accomplished by subjecting them to the action of 

 certain hardening or fixing solutions. The following are 

 most commonly used : 



Absolute Alcohol. Suitable for stomach, pancreas, and 

 salivary glands. These organs must be perfectly fresh, 



