THE MICROVIVISECTION METHOD. 125 



use of the mechanical stage by means of which the moist chamber 

 may be moved in two directions. 



The double holder, formerly manufactured by the Fowler shops 

 of the University of Texas, is twice as expensive as the single 

 holder. It possesses, however, the advantage that two needles or 

 pipettes may be used simultaneously. Each needle can be moved 

 independently of the other and either needle may be replaced by 

 a pipette. The manufacture of the holder has recently been dup- 

 licated by the mechanician of Wesleyan University under the 

 direction of Dr. H. B. Goodrich with modifications of his and my 

 suggestion. In setting up the apparatus, Dr. Goodrich introduced 

 the useful innovation of having the shelf to which the instru- 

 ment is clamped on a stand independent of the microscope. 

 The two stands are then clamped together on a common base. 

 The operator can thus shift the position of the instrument plac- 

 ing it at will in front of or on either side of the microscope. 



Fig. 2 illustrates the double holder as I have it set up. The 

 attachment of the instrument to the front of the microscope stage 

 facilitates manipulation of the screws with both hands. In the 

 illustration, a Spencer Lens Company lamp replaces the substage 

 mirror. As the heat of the lamp, however, produces undue evap- 

 oration and subsequent condensation in the moist chamber, it is 

 preferable to use the mirror. This necessitates raising the 

 microscope-stand on a block of wood so that the mirror can be 

 lowered below the microscope base so as to receive light unob- 

 structed by the lower screws of the dissecting instrument. 



The needle-carrier with its groove (Fig. 2, a), in which the arm 

 of the needle lies, is twice as long as in Barber's original instru- 

 ment. This extra length assists one in giving a straight even 

 movement to the needle when it is being pushed into the moist 

 chamber. After the needle has been thus adjusted by hand 

 approximate to its proper position, the plate b is pushed over the 

 arm of the needle and the screw c tightened to clamp the needle. 

 Further adjustment of the needle is carried out by the screws 

 e, f, g and h under the low and high powers of the microscope. 



In preparing the shelf on which the instrument is to be clamped 

 (Fig. 2,7) care must be taken that it be low enough to bring the 

 top of the carrier flush with the upper surface of the microscope 



