164 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



by boiling be used, in much less. I have cut, stained, mounted, 

 and diagnosed a tumour within three minutes. 



A microtome is necessary for the successful cutting of sections, 

 and the Williams and Swift patterns 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 in a thick 

 and syrupy solution of gum arable ; if time is no object it is a 

 great advantage to soak them in this for several hours. A block 

 is then placed on the corrugated plate of the microtome and 

 frozen by means of the ether spray which impinges upon it. 

 When the mass is nearly frozen a section is taken off by means 

 of a razor which is ground flat on one side, or the special knife 

 which may be obtained with the apparatus ; it is better to 

 moisten the upper surface of the knife with a little of the gum. 

 The section is carefully removed with a camel's-hair brush and 

 placed in a large vessel of clean water, so that the gum may be 

 dissolved out of it, and is then ready for staining. The block is 

 then raised by means of a very slight turn of the large milled 

 head under the apparatus, and another section cut. 



The mass must not be frozen too hard ; if this has Ijeen the 

 case, the necessary thawing will be hastened by gently breathing 

 on the block. If it begins to thaw, a few squeezes of the bellows 

 will bring it to the proper consistency. 



For extremely rapid work, the best method of freezing is by the 

 use of liquid carbon dioxide : this, however, is difficult in private 

 practice, owing to the unportability of the cylinders. The best 

 method is to use ethyl chloride or anaestile in metal cylinders, 

 such as are used for local anaesthesia. The best method is as 

 follows : Place a few drops of water on the plate of the microtome, 

 and freeze it solid by the ether spray whilst the surgeon is 

 removing the tumour ; cut a suitable slice off the latter and place 

 it on the layer of ice thus formed ; direct the ethyl chloride spray 

 downwards on to the slice, which will be frozen in a few seconds. 

 Unless the water be previously frozen on the plate of the microtome, 

 the block of tissue is very liable to slip, the lower portion being 

 frozen last. 



