84 THe MIcROSCcOPE. 
PICRIC ACID. 
Use a saturated solution in water. It will harden small 
pieces of tissue in 24 to 48 hours. It is especially useful for 
decalcifying foetal bones and for the study of cartilage. The 
pieces of bone and cartilage are left in the solution until a 
needle is readily passed through the bony structure.  Tis- 
. sues hardened in this reagent are stained a yellow color, which 
can be largely removed by prolonged soaking in water. The 
sections are easily stained with picrocarmine. 
OSMIC ACID. 
A ¥ per cent. solution is generally employed although 
stronger mixtures are sometimes required. It is best to keep 
a 1 per cent. solution on hand, and dilute it as required. It is 
a very poisonous and expensive reagent and is very liable to 
spoil by exposure to light. 
It is used to study the course of medullated nerve-fibres, 
as it blackens all fatty matters, and for many other tissues as 
recommended in the body of the work. 
DECALCIFYING SOLUTIONS—FOR SOFTENING BONE. 
Chromic acid —2-.=. 25... ee 1 gram. 
Witric acid, strong . 2422-2 -- ...-_-.2 ee 2@. €. 
Water te ob Se ek 200 ec. ¢. 
When a fine needle can be passed through the bone, it is 
removed from the solution and thoroughly washed in water, 
after which it is hardened in alcohol. The nitric acid removes 
the lime-salts while the chromic acid hardens the parts. The 
fluid should be frequently changed or what appears to answer 
as well, a few drops of nitric acid may be added from time to 
time if the softening process is delayed too long. 
HYDROCHLORIC ACID. 
A 12 per cent. solution will remove the lime-salts from an 
injected bone. 
PICRIC ACID. 
A saturated watery solution is very useful for decalcifying 
foetal bones. The mixture should be frequently changed or 
fresh crystals of the acid added. 
