wing by moving it forward or backward over one of the holes in the base plate 

 which receives its fastening screw. It may be that you are using a microscope 

 so built that the stage hits the bars even when the two instruments are lowered 

 to their limit in the pillar sockets. If so, raise your microscope off the manip- 

 ulator base plate by slipping under it a block of metal, bakelite, wood or any 

 firm material. Slip the moist chamber in the holder of the mechanical stage. Then 

 in each of the clamps, place one of the needle holders, with the screw end toward 

 you; the holders bein'g parallel to each other, and raised sufficiently so that 

 they are about ^ inch above the microscope stage. The apparatus is now assembled 

 for mounting the microneedles. 



Making and Mounting of Microneedles 



1. The Microburner. To make microneedles, it is necessary to have a very small 

 source of intense heat. A source of this kind is most readily constructed by 

 pulling out a 6 inch piece of 3 mm bore glass tubing in a Bunsen flame, so that 

 one end tapers quickly to a very fine point. If the point is sealed, open it by 

 gently breaking off the tip. Attach this tubing to a source of illuminating gas, 

 and light the flame. The jet thus obtained will probably be about 3 inches or 

 more in length. The opening must be reduced by gently approximating the lighted 

 end to a Bunsen flame. The aperture in the glass tubing will gradually diminish 

 in size, reducing the size of its flame. Continue until the flame is about ^ inch 

 long, with the gas turned full on. To secure finer control of the gas flow, a 

 Hoffman pinch-cock is clamped on the rubber tubing. A right angle bend in the 

 glass tubing is now made about three inches from the fine open end. The glass 

 tubing, point up, may now be fastened to a table by means of plasticine. 



£. The Microneedles. Over a Bunsen flame draw out a six inch piece of glass rod 

 to capillary fineness. The proper size of this capillary may be checked by insert- 

 ing a segment of it into the opening of the needle holder. The optimum diameter 

 is that which just permits easy fitting into the needle holder. I/Then a sufficient 

 supply of capillary rod has been made, break it up into six inch lengths, for 

 ease of handling. From these lengths of capillary rod, the microneedles are made 

 by pointing them over the microburner, holding the capillary horizontally with 

 the greatest part of its length in the left hand between thumb and index finger. 

 Grasp the right end of the rod with a pair of flat forceps, resting your closed 

 hands on the outer, fleshy part of the palm. Bring the rod over the microflame, 

 which should be about the size of a pin head, so that the rod is heated about \ 

 inch from the forceps. As the rod melts pull horizontally and smoothly until the 

 rod parts. This pulling action should at the same time remove the glass from the 

 flame. (See figure 4). 



T\ 9 .4 



