194 BACTERIOLOGICAL DIAGNOSIS. 
of tissue soaked in paraffin which is just melted for at 
least twelve, and more often twenty-four hours. To do 
this properly involves the use of some sort of an incu- 
bator. This might possibly be rigged up out of a tin 
biscuit-box in the manner already described, though 
considerably more heat would be necessary, as the 
paraffin melts at about 50° C. But the writer has often 
embedded the blocks by placing them in bottles con- 
taining the paraffin at such a distance from the fire that 
the paraffin is never completely melted, but always 
shows a thin solid layer on the surface. To do this it 
is only necessary to look at the bottle occasionally and 
move it a little further from the fire if the paraffin is 
completely melted and vice vevsé. ‘The process may be 
stopped at night without any harm resulting, and if the 
soaking only continues for a few hours at a time it is of 
no consequence so long as the total period is made up. 
CASTING THE BLOCKS. 
Special metal moulds are used in the laboratory 
(fig. 31). A pill box will do quite well. A small amount 
of melted paraffin is poured into the box and the piece 
of tissue is taken from the bottle containing the melted 
paraffin with a pair of forceps (previously warmed so as 
to prevent the paraffin from setting upon the points) and 
placed in the paraffin in the pill box. It is necessary to 
see that the surface from which’ sections are to be cut 
should be placed downwards. The box is then filled 
up with melted paraffin, and placed in a cool place or 
surrounded with water. The moment a firm film has 
formed over the surface the whole is plunged in cold 
water to hasten the setting of the paraffin; the more 
