CHAPTER XXXVIII 561 



hardest when in xylol or a clearing oil. FJatten or otherwise manipu- 

 late a fixed object, while it is still in weak alcohol, or it will break up ; 

 but some objects may be dissected successfully in clove oil. 122. 



(22) Cells alter soon after death: formalin fixation is the best for 

 corpse material. Carefully note 31. 



(23) The organs of animals over-anaesthetised by chloroform or ether 

 are often spoilt (especially in the vicinity of large blood vessels) and are 

 sometimes useless even for general purposes. 12. 



(24) Keep balsam or colophonium jar in the dark, or paint it 

 black outside. Acid balsam soon removes stains from tissue ; acid 

 balsam is the micrologists' bete noire. 443a. 



(25) After Zenker fixation sections may overstain in eosin. 



(26) If finished sections have crystals in them this is due to 

 improper washing out of fixative, or stain. 



(27) Formaldehyde gas dissolves in water up to 40 per cent. The 

 commercial formalin is acid and must be neutralised with magnesium 

 or sodium carbonate kept in a little bag in the stock bottle. 108, 



(28) Formaldehyde gas is injurious to the skin and mucous membrane 

 of nose. 



(29) If after staining in delicate dyes (e.g., methyl green), all the 

 colour keeps coming out of the sections during passage through 

 alcohols, try the following method : Wipe superfluous water from 

 around the sections, and dehydrate by dropping acetone on sections : 

 then plunge into a jar of half acetone, half xylol, then pure xylol. 



(30) For clearing embryos or pieces of tissue for whole mounts, cedar- 

 wood oil is better than xylol. 120. 



(31) If bubbles get under the coverslip they can often be removed by 

 gently warming, or by placing slide under bell jar of an exhaust pump. 



(32) If after mounting an object in balsam white or black lines and 

 blotchy areas appear, this means that dehydration was not complete. 

 Bring back through xylol to absolute alcohol. 



(33) When, after embedding, the block is set aside for a time and it 

 is found that the object is surrounded by a halo of white wax, this 

 means that all the clearing oil was not removed and is now exuding from 

 the object. Ee-imbed in pure wax. 



(34) When, after embedding, the material seems soft and tends to 

 fall out of the wax, this indicates that dehydration was not complete, 

 and possibly also that the time in pure wax was not long enough. 

 Without efficient dehydration it is impossible to make good sections. 



(35) If when cutting the sections curl up, it means that either the 

 knife is blunt or the material has been overhardened during imbedding. 

 Occasionally an incorrect slope of the knife may be the cause of 

 curling. 



(36) When the sections will not form a ribbon, this means that either 

 the wax is too hard or the slope of the knife is not correct. If the wax 

 is hard, place 1 drop of soft wax on each side of the block and flatten 

 it out with a warm knife. Read carefully pp. 83 to 90, 



(37) The broad side of a block sho'uld be parallel to the knife. 



(38) Some people use miniature drums for rolling up the wax ribbon. 

 Laying them on a piece of foolscap does quite well. Avoid sticky 



M. 36 



