560 A GUIDE FOR STUDENTS OF MICROTOMY. 



1050. General Rules and Hints for Students. (1) Keep all your 

 bottles and capsules as clean as possible. 



(2) Try to keep your bench in order (it is difficult, J. B. G.). 



(3) Keep notes of the time necessary for changing reagents. 



(4) Thoroughly clean your slides and coverslips in acid alcohol before 

 using. See addendum. 



(5) Note that corrosive sublimate tends to harden material. 



(6) Corrosive sublimate is difficult to remove from tissue unless you 

 use iodine. If not properly removed you will find numerous pin-shaped 

 crystals in the finished sections. 63. 



(7) Corrosive sublimate attacks the surface of steel and other metals. 

 Use quills, or wooden needles for manipulating tissue in sublimate. 



(8) Watery stains after picric acid fixation will cause maceration if 

 prolonged. 93. 



(9) Unless very well washed out, picric acid should not be used in 

 conjunction with thionin or toluidin blue. Precipitates form. Certain 

 other dyes do likewise. 



(10) Osmic acid crystals should be dissolved in the purest distilled 

 water. Wash the tube with distilled water before you break it, removing 

 label. Wash out capsules and bottles for osmic acid solutions in distilled 

 water. Keep solutions in shade or dark. 27. 



(11) Osmic acid tends to harden yolk and certain other cell materials. 

 The vapour of osmic acid is injurious to the eyes and nose. 



(12) Osmic acid and fixatives containing it inhibit staining, but if 

 necessary you can induce osmicated material to stain in delicate dyes 

 by bringing sections down to distilled water and treating in a -25 per cent, 

 solution of permanganate of potash for a short time. Permanganate 

 also decolorises sections. See page 31. 



(13) Nitric acid tends to soften chitin and yolk, but it may inhibit 

 staining a little. 97. 



(14) Imbed material in paraffin in the shortest time possible, for 

 materials left in the thermostat longer than necessary go hard, 

 especially from xylol ; this refers especially to vertebrate material and 

 yolky embryos. 



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

 dissolves away lipins. Vegetable oils dissolve fats less readily than 

 xylol or chloroform. Read 120 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 

 anything. The dregs are no longer absolute. Keep a waste alcohol 

 bottle for used liquid. 



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

 store bottles of absolute. This keeps the alcohol dehydrated. 



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

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



