42 THE ROYAL SOCIETY OF CANADA 



The Instrument. 



The apparatus used in cell dissection is shown in the accom- 

 panying figure. The moist chamber, which is open at one end and 

 with sides from 8 to 12 mm. high, is placed on the microscope so that 

 it may be moved about with the mechanical stage. The chamber is 

 roofed over with a specially cleaned coverslip, on the under surface 

 of which, the specimen is mounted in a hanging drop of Ringer's or 

 lymph fluid and held in place by surface tension. The dissecting 

 needle is made by drawing out one end of a piece of hard glass tubing 

 which is then bent at right angles, two or three millimeters from the 

 pointed tip. The needle-holder, a mechanism allowing of three 

 movements, is clamped to one side of the miscroscope stage, and the 

 needle is adjusted so that it projects into the moist chamber with its 

 tip pointing up into the hanging drop. By proper adjustment the 

 cell to be dissected and the point of the needle can be brought into 

 the same focal field. The three movements of the needle permitted by 

 the needle-holder and the two movements of the moist chamber by 

 the mechanical stage give the experimenter ample opportunity to 

 carry on dissection under the highest magnification of the microscope. 

 The dissecting needle-points can be made stiff and yet so fine that 

 their size bears about the same relation to that of a human red blood 

 corpuscle as an ordinary knitting needle does to the palm of the hand. 



Through the courtesy of the Biological Board of Canada I was 

 given in July 1917 the opportunity of continuirfg some microdissection 

 work at the Atlantic Biological Station, St. Andrews, N.B. I have to 

 thank Dr. Clara C. Benson for allowing me to take some material from 

 lobsters she was using for experimental purposes. 



Experimental. 



The ganglion cells of the Lobster. The ventral nerve cord was laid 

 bare and pieces of a nerve ganglion excised and placed on a thin 

 coverslip in a drop of lobster blood serum. This liquid is expressed 

 during a preliminary clotting of the blood and does not itself clot 

 for a considerable length of time. The nerve cells are carefully 

 isolated by teasing with needles under an ordinary dissecting micro- 

 scope. The coverslip is then inverted and placed on the moist chamber 

 so that the nerve cells lie in a hanging drop ready for microdissection. 

 The cell bodies lie among the closely interlaced nerve and neuroglia 

 fibers. When the fibers are torn away, the cell body may be isolated 

 with ease. 



The cell cytoplasm is very viscid in consistency and allows of 

 considerable tearing without disintegrating. Highly refractive spindle- 



