ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 167 



until the twist is taken out ; if twist is once taken out it should always 

 remain straight. When sharpening a knife it is rubbed away more at 

 the centre of the blade than at the ends, so it is necessary from time to 

 time, wlien the blade gets hollow, to rub it on the glass plate to make 

 level. In sharpening use a whetstone of good quality and as broad as 

 the knife blade is long, if you can get it, and keep the stone level by 

 rubbing it on the glass plate with emery and water. After floi^ding the 

 stone with water or oil, place the knife flat on it and rul) the knife 

 away from you with the back nearest to you and the edge away — that is, 

 the edge first in the direction of travel — until you get to the end of the 

 stone, then turn the knife over on the other side of the blade, this time 

 the back away and the cutting edge towards you, and draw the blade 

 along the stone towards you until you get to the other end of the stone. 

 Remember always to keep the cutting edge in front whichever way you 

 rul). Keep the stone covered with water or oil, and a sharp edge should 

 be obtained. For stropping use a strop fastened to a flat board, and 

 work the knife as a barber does when sharpening a razor. 



(4) staining- and Injecting:. 



Preparation and Staining of Material for Mitosis.* — A. E-^^r-:^ 



Openshaw says that instructive preparations for the study of .mitosis 

 may be obtained from the developing anthers of any of the ordinary 

 varieties of cultivated lilies or from the root-tip ^^C.ifee' onion. The 

 anthers from the immature bud should have the^tip^ut both ends cutoff 

 so as to allow of quick penetration of the fixing* fluid to the developing 

 pollen mother-cells. A solution ©f . 1 p.c. each of chromic and acetic 

 acids, or Fleming's weaker SQl-ution, may be used, and both are also 

 suitable for the root-tip. Air onion pfaced in a hyacinth-glass will soon 

 provide plenty of material. About a ^ in. of the tip should be cut 

 off and placed immediately in the fixative. After fixation for about 

 twenty-four hours the material should be washed free from all traces of 

 fixative, and passed through a series of alcohols of graduated strengths, 

 and then celloidinized. The sections may be stained by Delafield's or 

 Haidenhain's hoematoxylin, or Mayer's heam-alum, and very effective 

 double-stained preparations can be obtained by safranin and aniline 

 picrate. There is considerable variation and elasticity as to the time for 

 allowing the stain to act, and it is advisable to make experimental trials, 

 say to begin with, five minutes for Delafield or Mayer, and for 

 Haideuhain half an hour, in the mordant, and two hours in the stain. 

 With the double stain the safranin should be allowed twenty-four 

 hours, whilst a few minutes should suffice for the aniline picrate. 



Hsematoxylin Stain.f — A. G. Horny old communicates the following 

 haematoxyhn formula which he has used for some years with excellent 



- * Trans. Manchester Micr. Soc, 1915, p. 63. 

 t Lisbon, 1916. 



