EXPERIMENTAL EQUIPMENT AND PROCEDURES 



a micro-tlame of intense heat may be secured. The usual type oi micro-burner, 

 where the tube is drawn out to a thin tip of small bore, is not so likely to remain 

 uniform when in use. Hypodermic needles may be used as micro-flame tips. (See 

 illustrations following). 



2. Glass needles : There are two types of handles used for glass needles. The standard 

 type consists of a 7 mm. diameter glass rod cut into 10 cm. lengths by flaming longer 

 pieces in the center and drawing them out. In this manner one end of the rod is ta- 

 pered. The tapering end should be brought into the flame so that it retracts to knob 

 for attachment of the needle, made separately. See that the knob and rod are per- 

 fectly straight. Prepare 10 such needle handles. The second type of needle holder 

 consists of the regulation steel needle holder with adjustable screw into which various 

 needles may be inserted and fastened. This type is convenient and entirely satisfac- 

 tory. 



The needles may be made on the electric needle-puller but this is not necessary. 

 Secure some 4-5 mm. diameter soft glass rod and in a flame tip draw it out perfectly 

 straight until a thickness of about 1 mm. is secured. Break this into about 7-8 cm. 

 lengths and in the micro-flame, put a hook or a bend toward the end of each piece. 

 Hang this "hook" over any support (Metal rod) attached to the ring stand in such a 

 manner that it is directly above a 20 x 60 mm. (or larger) glass vial. In the bottom 

 of the vial place a small amount of cotton. At about 2 cm. from the base of the hang- 

 ing glass rod apply the micro-flame from the side. It will take practice to apply the 

 correct amount of heat. When the glass at the point of heat application is melted, the 

 weight of the hanging rod will drop it into the cotton in the glass vial, providing a 

 needle point of microscopic dimensions. With practice it may be possible to do this 

 in two steps, the first heating will lengthen and thin out the rod and the second will 

 draw an even finer point. In any case the tapering micro-point should not be long and 

 flexible and will probably have to be trimmed with sharp scissors. Draw out many 

 such needles at one time and mount them temporarily in plasticene, i. e. , until ready 

 to attach them to holders or to mount them in a needle board. These needle points 

 may be attached to the glass handles (described above) by bringing them together in 

 a small flame. The needles may be attached at a slight angle which will facilitate 

 operations. (See illustrations following). 



3. Steel needles : The ordinary steel needles are much too coarse for work with small 

 embryos. However, the finest Insect needles may be secured, cut short, and 

 mounted in wooden handles and will be extremely useful. 



4. Hair loops : This device is for handling embryos or isolated tissues. Draw out the 

 end of some 5-6 mm. soft glass tubing so that the total length is about 10 cm. and the 

 smaller end has a diameter of about 1 nnm. Close the larger end in a flame. The 

 smaller end should be cut off with a diamond pencil or flamed to make it smooth. 

 Secure some blonde hair fronn a newborn infant and cut it into 1 inch lengths. With 

 forceps insert one end of the hair into the capillary opening and then the other end 

 into the same opening. Regulate the insertion of the hair so that a relatively small 

 loop protrudes. Melt a small amount of soft paraffin on a glass slide and dip the 

 hair-loop into the paraffin, whereupon some of the paraffin will run up into the tube, 

 and harden upon cooling. This will hold the hair loop in place. To remove any par- 

 affin adherent to the hair loop itself, warm a slide in a flame, place on it a small 

 piece of filter paper, and gently touch the hair-loop to the filter paper. Avoid melt- 

 ing the paraffin within the capillary tube. 



5. Glass ball tip : This instrument is also used for moving embryos about without injury 

 to them. Using 6-7 mm. soft rod of about 18 cm. lengths, draw out the center (with 

 a flame tip) and break off the excess thread down to within 2-3 cm. of the widening 



