MICROSCOPICAL TECHNIQUE. 79 



minutes. Benzole and cedar oil are not so easy to remove as 

 chloroform, and it is necessary to remove all but a trace of the 

 clearing substance, otherwise the paraffin will be soft and bad for 

 cutting. The only modification entailed by the use of benzole or 

 cedar oil is that it is well to give two baths of paraffin, exhausting 

 during the first, but not necessarily during the second. This modi- 

 fication should not entail more than about five minutes' extra time, 

 if the paraffin is melted ready for use. Mr. Pringie recommends 

 an air-pump on the Tate principle, as it can be used for other 

 important purposes. He does not find that exhaustion facilitates 

 the hardening process, but thinks that further experiments are 

 necessary to settle the point. 



In the fixing, hardening, and embedding processes which he 

 uses and now recommends, the tissue is fixed in saturated HgClg 

 (corrosive sublimate) for about twelve hours, washed in running 

 water for a like time, and then put for twenty-four hours into 30, 

 50, and 70 per cent, alcohols consecutively, being kept in the latter 

 until further steps are to be taken. Mliller's fluid may be used in 

 the same way, followed by alcohols as above. Then the tissue is 

 placed in pure methylated spirit, absolute alcohol, and a second 

 time in absolute alcohol, each for twenty-four hours. Then chlo- 

 roform is placed with a pipette or syringe under the alcohol and 

 left twenty-four hours. This mixture is then poured away and 

 replaced by pure methylated chloroform, and the containing vessel 

 is left, loosely stoppered, on the top of the paraffin stove or in any 

 warm place for twenty-four hours, till any trace of alcohol has 

 vaporised. The tissue is then placed in the melted paraffin, and 

 the air-pump may come into use as soon as the tissue has warmed 

 through. 



Fixing Paraffin Sections to the Slide."^— Dr. G. L. Gulland 

 uses a modification of Gaskell's method. The paraffin block con- 

 taining the tissue must be trimmed very carefully, care being taken 

 that the surface meeting the razor is exactly parallel to the opposite 

 surface, and that the block is exactly rectangular. A thin layer of 

 soft paraffin is then applied to the surface meeting the razor and to 

 the opposite surface. This is best done by dipping these surfaces 



* Journ. Anat. and Physiology^ xxvi. (1891), pp. 56 — 59. 



