442 E. A. MINCHIN ON SOME DETAILS IN THE ANATOMY OF 



be dissolved out. I do not propose to describe any details here 

 which cannot be verified by an observer possessing a dissecting 

 microscope * and a pair of mounted dissecting needles and a 

 flea ! In fact the results obtained by me and set forth here are 

 based entirely on what may be termed " needlework." 



Before proceeding to anatomical descriptions, I may give a 

 brief account of the technique I have employed. The flea at 

 liberty is, I need not say, an active and elusive insect. But 

 when placed on the surface of water, he is perfectly helpless, and 

 floats there without being able to escape and without drowning 

 for at least twenty-four hours, provided there is no soap in the 

 water ; if there is a trace of soap the cuticle of the flea is wetted 

 and the insect sinks and is soon drowned. (This hint may be 

 borne in mind as being often useful in the home.) 



Having therefore caught your flea, put it on the surface of 

 some water and keep it until you can proceed further with your 

 operations. An expeditious way of catching the flea is to get 

 it to hop straight on to the surface of water. In doing this 

 remember that a flea always hops by preference away from the 

 source of light, never towards it. 



When it is desired to dissect the flea it should be gathered off 

 the surface of the water with a fine forceps and placed in a drop 

 of physiological salt-solution (0*75 gramme sodium chloride in 100 

 cubic centimeters of distilled water) on an ordinary microscopical 

 slide, which is then placed on the stage of the dissecting 

 microscope. 



For the dissection I use two fine needles mounted in wooden 

 handles. Each needle after fixing in the handle is ground down 

 further on an ordinary hone. One of them is ground to a fine 

 sharp point, the other to a flat cutting edge. For preparing the 

 flat-edged needle, I first take a penknife and pare the extremity 

 of the wooden handle on both sides so that it is shaped like an 

 ordinary brad-awl. I then rub the needle down on the hone in two 

 planes parallel to the two cuts made in the handle, checking the 

 process under the dissecting microscope and trying to get a 

 rounded cutting edge, not an edge which terminates in a straight 

 line like an ordinary chisel. The object of paring the wooden 

 handle is both to guide the hand when rubbing down the needle 



* I have used in all my work a Greenough binocular dissecting 

 m'croscope made by Zeiss. 



