FIXING MATERIAL FOR CUTTING l8l 



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 sufficient to say that they should never 

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

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

 of less importance. 



The bulk of the fluid in which the block is placed should be at 

 least twenty times that of the block, and it is not advisable to 

 place two blocks in the same vessel. 



The fluids which we shall recommend for this purpose are : 



I. Perchloride of mercury in normal saline solution. This is 

 prepared by dissolving common salt in water in the proportion of 

 7 grammes to a litre (about 3J grains to the ounce), and saturating 

 this solution whilst hot with perchloride of mercury. The 

 solution must be allowed to cool completely ; as it does so, 

 crystals of the mercury salt will separate but. 



This fluid fixes completely in twenty-four hours, or less, and 

 gives most excellent results. Its powers of penetration are not 

 very great, so that slices of tissue which are to be fixed in it 

 should be thin. 



The after-treatment of the blocks fixed in this fluid must be 

 described briefly. They are allowed to remain in the solution for 

 twenty-four hours and no longer, and are then washed for twenty- 

 four hours in running water to remove the perchloride of mercury. 

 They are then passed through the various strengths of spirit (as 

 will be described subsequently), a little tincture of iodine being 

 added to each to remove any mercury which may still remain. 



