188 BACTERIOLOGICAL DIAGNOSIS. 
the infiltration processes, but are prepared very rapidly, 
and are often sufficient for diagnostic purposes, where 
rapidity is the first consideration. 
The blocks of tissue must be hardened before being 
cut, any of the above fluids being applicable; where 
alcohol is used it must be washed out in water, as it will 
not freeze. Where more rapid work is required the best 
method is a modification of the old boiling process, as 
revived by Mr. Strangeways Pigg. The slices of tissue 
from which sections are to be cut are thrown at once 
into boiling water and allowed to boil vigorously for two 
or three minutes; the water must be actually boiling 
when the tissues are added, and the bulk used should 
be large as compared with the block. The tissues are 
then rapidly cooled by being thrown into cold water, 
and are then ready for cutting. The outer surface of 
the block should be rejected. 
This method of fixation leads to a little distortion of 
the tissues and alters any blood which they may con- 
tain, but it is very good for diagnosing tumours. It is 
invaluable in the post-mortem room, and for diagnosis 
of the nature of a tumour during operation. In skilful 
hands a section may be cut, stained, mounted, and a 
diagnosis made in ten minutes. 
A microtome is necessary for the successful cutting of 
sections, and the Williams and Swift pattern are those 
in general use for the freezing process. We shall 
recommend the practitioner who intends to take up 
this branch of work to procure a Cathcart microtome, 
which is exceedingly cheap (it costs about a guinea) 
and answers admirably. The great advantage of this 
machine is that it will serve for cutting sections in 
paraffin as well as for frozen sections. 
The blocks of tissue which are to be cut are dipped 
