MICROSCOPICAL TECHNIQUE. 89 



6. — Rinse sections in ordinary water for one minute. Red 



clouds are given off and the sections become bluish. 

 7. — Place slides for two minutes into water slightly acidified 



with acetic acid. This is done to deepen and fully restore 



the blue colour, and also to fix the eosin. 

 8. — Dehydrate, clear with xylol (not clove oil), and mount in 



turpentine balsam." 



Preparing and Mounting Head and Proboscis of Blow-Fly.*— 



Mr. T. J. Body thus describes his method : — " First catch the 

 flies ; kill them with chloroform and their tongues will protrude ; 

 cut the heads off and drop them into a vial of strong carbolic 

 acid ; let them remain there a few days or until a convenient time ; 

 take a head out of the vial, and place it on a glass slide or slip ; 

 puncture the head with a needle, and put over it another slide and 

 press it flat ; separate the slips and clean them off (do this several 

 times) ; place the object on the stage of the dissecting microscope 

 and examine it carefully ; remove all loose, extraneous matter from 

 around the head ; if the tongue is crooked or the antennae are 

 folded over, place them in the position in which they are to 

 remain ; then press again between two slips and put on a clip, and 

 let it remain so until the next evening (I do all my work in the 

 evenings) ; soak again for a day or two in carbolised turpentine ; 

 wash well in water to remove the acid, using a camel's-hair brush 

 for this purpose ; then dry between two slips, say, for a day or so ; 

 then soak in clove oil until ready to mount. Prepare a cell of 

 gold-size to suit a 5/8 or 3/4 cover glass some two weeks or more 

 in advance of the time for using it. Remove the object from the 

 clove oil, and remove all the oil possible with blotting-paper 

 without touching the object. Put a small drop of benzol balsam 

 on the centre of the slide, and with a wooden toothpick or needle 

 spread it so as to cover the space within the cell ; place the head 

 in the centre of the cell and drop a small drop of benzol balsam 

 on it ; this will just fill the cell nicely, but it will be a little high in 

 the centre. Place a clean, warm cover as nearly central as pos- 

 sible, and let it fall of its own weight ; if the balsam is a little 

 thick, some gentle pressure may be used, and when the cover is 



* The Observer {Practical Microscopy), vi., 1895, PP- 5^— 57' 



