l88 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 



