FIXING MATERIAL FOR COTTtNCi l6l 



for ordinary purposes cannot compare with paraffin for beauty of 

 results and facility of application. 



In the paraffin process the tissue is infiltrated throughout with 

 hard paraffin (such as is used for the better varieties of paraffin 

 candles), so that every cell and every fibre is permeated and 

 supported on every side. To do this requires a number of 

 processes. It would be of no use to immerse the block of tissue 

 in the paraffin just as it is, for the paraffin would not wet it, much 

 less soak into it. The water is first removed ; and this is done by 

 soaking the material in absolute alcohol. But alcohol does not 

 dissolve paraffin or mix with it ; it is therefore necessary to remove 

 it by means of some fluid which will mix with it on the one hand 

 and paraffin on the other. Of these there are many : xylol, 

 chloroform, benzine, cedar oil, and many more are in use for 

 special purposes. Chloroform answers most purposes, and is to 

 be generally recommended. The block of tissue is now ready to 

 be soaked in melted paraffin ; it is kept in a bath of this substance 

 until the chloroform has been entirely driven off and replaced by 

 the paraffin. The whole is then allowed to cool, is shaped into 

 suitable blocks, and is then ready for cutting. 



We shall now describe the processes in fuller detail. 



FIXING MATERIAL FOR CUTTING 



These processes must be understood by all practitioners, even 

 although they do not intend to cut sections for themselves. It 

 happens to every medical man to find it necessary to send tumours, 

 etc., to a laboratory to obtain a pathological diagnosis; and in 

 very many cases the materials are treated in a way which 

 absolutely prevents good sections being obtained. Many fixing 

 fluids are in use, and any of them may be selected, but it is 

 absolutely necessary that the material to be investigated should be 

 cut into small pieces and put into a large bulk of the fluid at once. 

 This is especially necessary in the case of material removed at a 

 post-mortem examination, where the tissues and organs have 

 already undergone alteration. 



As regards the size of the slices which are to be placed in the 

 hardening fluid, it is sufficent to say that they should never 

 exceed i inch in thickness, and if perchloride of mercury is used 

 should be even thinner. The other dimensions of the block are 

 of less importance. 



