CHAPTER XXXVL 507 



an ordinary ether-alcohol solution and evaporate off the solvent 

 in the oven overnight. 



It takes many days to dissolve thoroughly, but the time may be 

 shortened by keeping it at 90 F. Fix objects in absolute alcohol ; 

 bring them into clove oil, and allow this to clear the preparations, 

 then transfer to the clove oil celloidin. The time in this must be 

 gauged according to the size and nature of the insect ; fleas, if a 

 rupture is made in the chitinous covering, are penetrated in twenty- 

 four hours or less. When ready to embed, dip a cover-glass in melted 

 paraffin wax, to get a smooth surface on which the celloidin solution 

 will not spread, but forms a thick drop. Place the insect on the 

 prepared glass slip in a drop sufficient to completely cover it, and 

 arrange in any desired position. Invert the cover-glass and float 

 on to some chloroform ; leave for half an hour or longer, according 

 to the size of the drop. The drop of celloidin should fall away from 

 the glass. Transfer to melted wax, and allow time for the wax 

 thoroughly to permeate (twenty minutes is long enough for fleas 

 and lice). The result will be a small tablet-shaped mass of spongy 

 celloidin impregnated with wax ; this can be at once embedded, or 

 may be put away for future use. (Professor Boycott informs me 

 that he has never left his preparations for more than two or three 

 weeks at a time, so that he has no data as to how long the same could 

 be kept, but they could probably be stored indefinitely.) 



945s. Carbon Bisulphide Embedding of Insects, etc. HEIDENHAIN 

 many years ago recommended carbon bisulphide as a medium for embed- 

 ding in wax. This fluid is both smelly and dangerous and should only be 

 used in electric thermostats. The wax is dissolved in carbon bisulphide, 

 and dehydrated insects, etc., are placed in some of the fluid which is 

 allowed to evaporate at a gentle warmth. Subsequently the material 

 is rapidly treated in pure wax in the thermostat. This method cer- 

 tainly curtails the length of time in the thermostat, and overheating is 

 a serious matter when one is working at chitinous or brittle organisms. 



946. Test for Chitin (ZANDER, Pfliigers Arch., Ixvi, 1897, p. 545).- 

 Treat for a short time with a drop of freshly prepared solution of iodine 

 in iodide of potassium and add a drop of concentrated chloride of zinc. 

 This is then removed with water as far as possible, and the violet 

 reaction is obtained. 



See also WESTER, Zool. Jahrb., Abth. SysL, xxviii, 1910, p. 531. 



947. BETHE'S Stain for Chitin (loc. tit., 945). Sections are put 

 for three or four minutes into a freshly prepared 10 per cent, solution of 

 anilin hydrochloride, to which has been added 1 drop of hydrochloric 

 acid for every 10 c.c. They are then rinsed in water, and the slide is 

 put with the sections downwards into 10 per cent, solution of bichro- 



