52 PROTOPLASM 



slide on which are cemented (with balsam) two glass bars 5 cm. 

 long, 8 to 10 mm. high, and 2 to 4 mm. thick, placed slightly 

 less than 24 mm. (the width of a cover slip) apart (Fig. 36). 

 The two needles may enter at one and the same end, as in the 

 old Barber-Kite or the Chambers apparatus; or at both ends, 

 as in the Taylor and Peterfi instruments. The chamber is 

 held in a mechanical stage, which is used almost as much in 

 the process of dissection as are the needles, since it is often 

 more convenient to grasp the material with a needle and then 

 move it by means of the mechanical stage than to move the 

 needle. 



:^ 



B 



£ 



c 



Fig. 39. — A, Glass rod preliminary to making a needle; B, C, types of needles; 



D, micro-spatula. 



The next task of the micrurgist is to make his needles, and 

 this is the most difficult part of the technique for a beginner, 

 though it does not long remain so for those who have patience 

 and some dexterity. The needles may be made of glass tubing 

 or rod. The latter is better, as a broken tip leaves the needle 

 point still usable. 



Hard (Jena) glass is usually preferable to soft glass but not 

 necessary for ordinary work. Quartz may be used, giving 

 very tough points, but it requires intense heat to draw it and, 

 except for special work, is not worth the trouble. The rod 

 should be three or four millimeters in diameter. It is first 

 drawn in the flame of an ordinary Bunsen burner to the shape 

 shown in Fig. 39 A; next, the thin central region is drawn 

 still finer in the very minute flame of a microburner; the finely 

 drawn portion is now held near (not in) the microflame until 

 the right degree of softness (a dull red color) is reached. When 

 sufficiently soft, the thin rod will give way under the pull of 

 the hand; it must be quickly drawn so as to form a rapidly 

 tapering point (Fig. S9B). A good needle should not be over 

 In at the tip and should taper correctly so as not to be too 

 flexible or too heavy. Different types of needles will naturally 



