164 
PRACTICAL PHOTO-MICROGRAPHY. 
take longer time than the gum, for tissues to be cut in 
gum require to be more hardened than those to be cut 
in paraffin, according to our experience. If we have a 
tissue properly prepared for embedding in paraffin, 
we look upon it as a certainty that we shall get good 
sections. 
The tissue, supposed to be in seventy per cent, 
alcohol, is soaked for twenty-four hours in “neat” 
methylated spirits, then for two periods of twenty-four 
hours each in fresh absolute alcohol. Then with a 
pipette methylated chloroform is put under the alcohol, 
and the tissue is left there till it sinks down into the 
chloroform, or for twenty-four hours. It is next soaked 
for twenty-four hours in chloroform, the tube containing 
it being kept in a warm place and loosely stoppered. 
Mineral naphtha may be used in place of, and in the 
same way as, chloroform. We prefer these volatile 
substances to cedar oil and the like, in view of the 
exhaustion process which is to follow; but if this process 
is not to be performed, cedar oil is the best paraffin- 
solvent to use. We place the oil at the bottom of the 
tube, on it we pour carefully sufficient absolute alcohol 
to cover the piece of tissue, and on the alcohol we care¬ 
fully place the tissue taken out of the second dose of 
absolute alcohol. When the tissue has sunk down into 
the oil it is put into the oil alone, and left till it is clear, 
the oil having then fully impregnated it. 
After the chloroform, the naphtha, or the oil, the 
tissue is placed straight into melted paraffin ; we can 
discover no use for intermediate baths of paraffin in a 
