Examine the needle point under the compound microscope by laying it very carefully 

 on a clean glass slide and bringing it into the field. A well made needle will have 

 a fine, sharp, rapidly tapering point. If the heat has been too intense, or the pull 

 has been too rapid, an extremely long and fine flexible "hair" will result. If the 

 heat has not been sufficient, the glass will break, giving a blunt, jagged, unser- 

 viceable point. A typical, well made needle is shown in figure 5. 



Make one dozen of these microneedles in this manner leaving a three inch shaft, and 

 place in the needle block. The block may be made of any wood about \ inch thick, and 

 convenient size, (6 inches by 3 inches) in which holes have been drilled, 1/8 inch 

 in diameter, \ inch deep, and \ inch apart. Bring the needles to your instructor 

 for criticism and inspection. 



3. Bending the Microneedles. Needles which have been approved should now be bent at 

 an angle. This is done by carefully applying heat not more than 5 mm from the tip 

 and pushing upward with a steel needle or fine forceps. The angle of bending varies 

 with the use in view. It has been found satisfactory to work with needles of two 

 types. (Figure 6). 



B <£ 



Fi*. e 



In type A, there is a single bend of about 60 degrees. In type B there is a double 

 bend, the second one carrying the point back over the shaft. CARE MUST BE TAKEN 

 DURING THE BENDING OF NEEDLES TO PROTECT THE SHARP POINT FROM MELTING IN THE FLAME. 



4. Steps Preliminary to Mounting and Use of Microneedles. 



(a) Turn the three screws (G, H and I) of both manipulators four or five revolu- 

 tions until the bars are slightly separated. This will allow movement in 

 two directions in each of the three planes. 



(b) Use your #lb Leitz objective with lOx ocular. 



- (c) Make sure that your lighting system gives you sufficient illumination and 

 that a heat screen is interposed. 

 (d)--Wet with distilled water the strips of blotting paper along the sides of 

 the moist chamber. Grease the tops of the side bars sparingly with vase- 

 line, and put a cover slip in place. Rack the moist chamber back until 

 the condenser lens is cleared. 



5. Mounting the Microneedles. Test the operation of the screw on the end of a needle 

 holder. Insert a needle of type A in the left holder. If the needle is clamped in 

 too tightly the snaft may be broken. Should this occur run a wire through the lumen 

 to clear it of broken glass. Slide the needle holder forward until the needle tip 



