ANATOMICAL AND PATHOLOGICAL TISSUES. 1053 
It therefore becomes necessary to keep such preparations in a 
semi-dark atmosphere, except when being used for purposes of 
demonstration. 
The following is briefly the method of procedure :— 
Before subjecting the tissues to the preserving fluid, it is 
necessary to avoid, as far as possible, any contact with water; and 
so, instead of washing them in water as was done formerly, they 
are merely wiped dry with a piece of cloth. 
They should then be placed immediately in a solution con- 
sisting of — 
Commercial Formalin, parts 5-10 (40 per cent. Formic alde- 
hyd.) ; Chloride of Soda, part 1; Sulphate of Soda and 
Sulphate of Mag. in equal proportions, parts 2. 
made up with water to 100 parts. 
The length of time during which they should be subjected to 
this fluid varies with the size, thickness, and consistence of the 
tissue. 
Objects of the size of spleen and kidneys (normal) require about 
two days, and the fluid should be changed twice during that time. 
Large objects require a longer subjection to the fluid, the time 
varying directly with the size and thickness of the organ. 
The fluid, during the process, becomes of a dirty brownish-red 
colour ; when this is seen fresh fluid is required. 
It is particularly necessary that all parts of the tissue should 
be brought into contact with the fluid, and that the object should 
be given the shape and position which it is desired that it should 
retain permanently. 
While in the solution the organs change colour, and assume a 
dirty bluish-grey appearance. 
This colour is, however, discharged on placing them in 95 per 
cent. alcohol, and the normal colour returns. 
Before placing them into alcohol they should be washed 
thoroughly in alcohol until the latter no longer becomes cloudy. 
Tt must on no account come into contact with water. 
Tt should be left in alcohol for a period sufiiciently long for the 
normal colour to return, and no longer. 
Tf left too long in this fluid the colour is removed. 
As soon as the colour has completely returned, it is placed in 
the permanent mounting fluid, and for this purpose we find that 
the best solution consists of equal parts of glycerine and water. 
Tn this fluid the material at first floats, but as soon as it becomes 
thoroughly impregnated it wiil sink to the bottom. 
After a short time the mounting fluid begins to assume a 
yellowish colour. It should then be canged and fresh fluid sub- 
stituted. 
