A GUIDE FOR STUDENTS OF MICROTOMY 127 



(15) Alcohol and chloroform dissolve fats and lipoids, acetic acid 

 dissolves lipiiis. Vegetable oils dissolve fats less readily than xylol 

 or chloroform. Read §§ 133 et seq. 



(16) Strong alcohol is bad for the finger nails and skin. 



(17) When diluting stains with alcohol, use solutions made up by 

 breaking down pure absolute alcohol. Do not use methylated spirit, 

 as this generally precipitates the stain. 



(18) You can soon learn to tell roughly the strength of alcohols by 

 the smell. 



(19) Don't use the dregs of the absolute alcohol bottle for dehydrating 

 anj'thing. The dregs are no longer absolute. Keep a waste alcohol 

 bottle for used liquid. 



(20) Some workers add a little bag of fused copper sulpliate to their 

 store bottles of absolute. This keeps the alcohol dehydrated. 



(21) After fixation, when dehydrating and imbedding a piece of 

 tissue, an egg or an embryo, it is at its softest when in weak alcohol, and 

 its hardest when in xylol or a clearing oil. Flatten or otherwise mani- 

 pulate 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. § 8. 



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

 corpse material. Carefully note § 33. 



(23) The organs of animals over-ana*sthetised by chloroform or ether 

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

 sometimes useless even for general purposes. 



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

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

 the microtomists' bete noire. §§ 483 and 499. 



(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. § 113. 



(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, chloro- 

 form, carbon bisulphide, or cedar- wood oil are better than xylol. § 133. 



(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 imbedding, 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. Re-imbed in pure wax. 



(34) When, after imbedding, 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. W^ithout 

 efiicient 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) WTien the sections will not form a ribbon, this means that either 



