374 
Transactions of the Society. 
The basic principle of the instrument consists in rigid bars 
which are screwed apart against springs. The movements imparted 
are in arcs of a circle having a radius of about in. As the 
extreme range of movement of the fine adjustments is only 2 mm. 
(of which only one is necessary) the curvature of the arc is un- 
noticeable. 
The movements performed by the instrument are so accurately 
controlled that one can readily carry out such delicate operations 
as puncturing mammalian blood corpuscles, tearing off the sarco- 
lemma of a muscle fibre, drawing out nuclear chromatin strands,, 
and even cutting up the chromosomes of insect germ-cells. The 
glass needles used for these operations taper rapidly to a point 
invisible under the oil-immersion objective. With the micro- 
pipette, the bore of which need be no larger than one micron in 
diameter, one can either inject substances into or withdraw 
material from a cell. 
For the isolation of bacteria the instrument is not only steadier 
than Barber’s apparatus, but has new features which facilitate 
greatly the method of procedure. The application of this instru- 
ment for bacteriological purposes is more specifically dealt with in 
the Journal of Bacteriology and the Journal of Infectious Diseases. 
I take this opportunity of expressing my deep obligation to 
Mr. W. Farnham, mechanician in the Department of Mechanical 1 
Engineering in Columbia University, to whose skill and faithful 
workmanship the practical evolution of the instrument is due. I 
’wish also to express my appreciation to many friends for valuable 
suggestions. The principle involved in the construction of the 
micro-manipulation instrument is patented. 
2. A Mechanical Micro-Manipulator for Controlling the 
Movements of a Micro-Needle or Micro-Pipette in 
the Field of a Compound Microscope. 
The principle of this device is demonstrated on considering the 
mechanism for the movements in one plane only (fig. 15). This 
consists of three bars of rigid metal connected at their ends to 
form a Z-like figure by resilient metal acting as a spring hinge. 
By the action of certain screws the bars can be forced apart ; 
on reversing the screws the bars return to their original position 
owing to the spring action at the end of the bars. By these means 
arc movements may be imparted to the tip of a needle when placed 
in the proper position. 
The needle or any instrument the tip of which is to be 
manipulated is held in a carrier fastened to the free end of a bar 
A at x. The needle is made to extend so that its tip is at the 
apex of an imaginary triangle at D. In order to obtain two move- 
ments at right angles to one another and in the horizontal plane 
