286 NATURE NOTES. 
above it is apparent that an investigation of this kind has 
many difficulties to overcome. Scattered in the indices of 
the scientific journals many references will be found relating 
to the subject, but few data of an exact experimental kind 
is available. 
Another way by which the problem may be attacked is 
to protect the structures from change, by means of a trans- 
parent envelope. I attempted it in this way :—Drop the 
specimen into a weak solution of sodium chloride in 
water (0°25 per cent.) containing a trace of mercuric chloride 
(1 in 5000) kept at or just below the boiling point, the inverted 
Specimen being weighted by means of a glass rod. It is 
kept in this for a few minutes, to expel air and saturate tissue 
superficially, quickly withdrawn, allowed to dry externally, 
then coated by immersion in a thin celluloid varnish, which 
dries immediately, leaving a thin transparent varnish. The 
results, at least in the case of soft structures, are not of 
much practical value. 
In the absence of exact data hinted at above, one has to 
fall back on the empirical. One of the most useful all-round 
preservatives is formaldehyde, familiarly known, in its 40 
per cent. solution in water, as formalin. It has the merit 
of being cheap, requires no skilled manipulation, and when 
used with care has many fairly satisfactory applications. 
When there is an absence of brilliant tints and marked 
contrasts a one per cent. solution in water does well; but when 
the colours are intense and contrasted, a weaker solution is 
more advantageous, say 1 part in 500 parts of water. In 
strong solution, intense blues and yellows lose their 
brilliancy, red becomes deepened in tint. A sea-urchin 
which was dredged two years ago off Millport and put into 
weak formalin solution the same day, retained the delicate pink 
tints seemingly unimpaired. Of the many ways tried, the 
one that seems to have the most general application consists 
in the combined use of Joré’s Fluid, spirit and glycerine. 
Joré’s Fluid has the following composition :— 
Sodium chloride, . i 5 1 part. 
Sodium sulphate, . : 2 parts. 
Magnesium sulphate, : Zr, 
Bolutien of formalin (10 per feat) ROO. Mes, 
