2l6 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



blocks should be cut small and placed at once in methylated 

 spirit diluted with an equal quantity of water. Five per cent, 

 of formalin may be added with advantage. 



SECTION-CUTTING BY THE FREEZING METHOD 



Sections which are prepared by the freezing method are 

 rarely as thin as those prepared by one or other of the infiltra- 

 tion 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. 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 contain, 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; 

 or if no process of fixation by boiling be used, in much less. 



A microtome is necessary for the successful cutting of sec- 

 tions, and the Williams and Swift patterns are those in general 

 use for the freezing process. We shall recommend the prac- 

 titioner who intends to take up this branch of work to pro- 

 cure 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 w r ell as for frozen sections. 



The blocks of tissue which are to be cut are dipped in a 



