6 NORMAL HISTOLOGY. 



pearance, and stains fat and certain allied substances 

 deep black. It is used in one-per-cent. aqueous 

 solution. The tissue should be quite fresh when 

 immersed in it, and, as a rule, should remain for 

 twenty-four hours. Specimens hardened in osmic 

 acid commonly become quite granular and dark 

 after a time. 



Preservative fluids are sometimes brought into 

 more direct contact with the tissues, by injecting 

 them into the blood-vessels of the part before cut- 

 ting it in pieces ; or they may be driven directly 

 into the interstices of the tissue, by means of a small 

 syringe with a sharp-pointed canula ; this is called 

 interstitial injection. 



Indications as to which of these agents are best 

 adapted for the preservation of different tissues, and 

 the more exact details of the methods of employing 

 them, will be given as we proceed with our practical 

 study. 



STAINING AGENTS. 



Hcematoxylin is one of the most generally useful 

 of the staining agents. It has the power of coloring 

 certain parts, as the nuclei of cells, deeply, while 

 other parts are stained much less, or not at all. 

 The following is Delafield's method of preparing the 

 solution : To 100 c. c. of a saturated, aqueous solu- 

 tion of ammonia alum, with an excess of alum 

 crystals, add I grm. of haematoxylin (Merck's is 



