INTRODUCTION. xxxiii 



as it blackens the myeline. Small pieces of tissue exposed to the vapour of a one per cent, 

 solution for a few minutes, are easily stained with picrocarmine, though the prolonged action 

 of a strong solution renders subsequent staining difficult. It is one of the most useful of 

 all hardening reagents (M. Schultze). It is not necessary to mount preparations treated with 

 osmic acid in a saturated solution of acetate of potash. 



METHODS OF SOFTENING TISSUES. 



Certain tissues, as bone and tooth, which contain calcareous matter, require to have the 

 calcareous matter removed before they can be conveniently cut for the microscope. This is 

 done by placing them in a decalcifying solution. Some solutions remove only the calcareous 

 matter e.g. dilute hydrochloric acid without at the same time hardening the tissue ; others, as 

 a mixture of chromic acid and nitric acid, remove the lime salts, and at the same time harden 

 the tissue, and generally the latter are to be preferred. 



DECALCIFYING SOLUTIONS. 



1. Hydrochloric Acid. Mix one part of strong acid with ten parts of water. This does 

 very well for the removal of lime salts from an injected bone. 



2. Chromic and Nitric Acid Fluid. Make a \ per cent, solution of chromic acid, and to 

 every 100 c.c. add I c.c. of strong nitric acid. The chromic acid solution is easily made by 

 adding an equal volume of water to a one per cent, solution (p. xxxi). This fluid takes two' or 

 three weeks to remove the lime-salts from a small piece of bone, but if the fluid is frequently 

 changed the result is accomplished more rapidly. The tissue is then thoroughly washed to 

 get rid of the acids, and then hardened, first in weak and then in strong methylated spirit. 

 The advantage of this fluid is that the chromic acid hardens the parts, whilst the nitric acid 

 removes the lime-salts. Bones, after being exposed to its action, assume a green colour, owing 

 to the formation of a sesquioxide of chromium. 



3. Picric Acid Solution. A saturated watery solution takes several weeks to act on a 

 moderately large piece of bone. It is of great value for fcetal bones. 



4. A 10 per cent. Solution of Common Salt and Hydrochloric Acid. This is most valuable 

 for showing the matrix of bone, which consists of ordinary fibrous tissue, and swells up in the 

 ordinary acid media. A 10 per cent, solution of salt prevents this (v. Ebner and De B. Birch). 

 The bone is placed in a 10 per cent, solution of common salt, to which i to 3 per cent, of 

 hydrochloric acid is added. Add from day to day as much acid as will decalcify the bone. 

 When the bone becomes flexible it is placed for several hours in water, to remove all the acid. 

 Leave it for several days in 10 per cent, salt solution, which must be changed repeatedly. 

 When the reaction of the bone becomes neutral the bone is white and opaque. Sections are 

 made, and mounted in a 10 per cent, solution of salt. They show the fibrillar structure of the 

 matrix (p. 32) (v. Ebner). 



