APPENDIX 295 



II. METHODS OF HARDENING AND PRESERVING 

 TISSUES. 



a. The tissues should be removed from the body to the 

 hardening agent as soon as possible after the death of the 

 animal. 



The tissues should not be allowed to soak, either in or out of 

 the body, in blood, serum, lymph or normal salt solution. 



In many cases the tissues may be left in the body for a day after 

 death, provided they are not surrounded by any excess of fluid. It is 

 in fact easier to obtain the peripheral nerves (osmic acid) and the 

 central nervous system (Marchi's method) without injury a day after 

 death than in the fresh state. 



If any blood or fluid is on the tissue, it should be removed 

 by placing the tissue on blotting-paper. 



The tissue should be divided with a sharp razor, into as small 

 pieces as is consistent with obtaining all the parts required for 

 examination. As a rule the pieces should be only 2 to 4 mm. in 

 thickness. But very soft tissues such as the brain are gene- 

 rally placed whole in the hardening agent ; they may be sliced 

 as soon as the surface is sufficiently hardened, but such slices of 

 the brain are apt to buckle. 



The volume of the fluid should be 15 to 20 times that of the 

 tissue. When a piece of tissue is kept days or weeks in a 

 hardening agent, such as Mutter's fluid, the fluid should be 

 renewed in 1 day, and once or more later. 



The tissues should be placed in a flat short bottle rather than 

 in a narrow high one, unless they are suspended in fluid ; 

 they should be kept cool for the first day or two, then they may 

 be warmed if it is desired to hasten the process of hardening. 



b. Treatment after the primary hardening agent. After 

 treatment with the primary fixing or hardening agent, the excess 

 of the agent is in nearly all cases removed from the tissue. 



