MACHINERY OF INSECT FLIGHT 135 



muscle, weights were attached to the piece of metal. Changes in length 

 were recorded by a second transducer coupled to the metal strip by a light 

 spring. The tension recorder was connected to the oscilloscope to give 

 vertical deflections of the beam and the length recorder to produce hori- 

 zontal deflections. The tension-length relations of the muscle were there- 

 fore drawn out instantaneously on the screen. 



?" 



V]S. 



0.5 0.7 0.9 



LENGTH '«'" 



Fig. 9. Tension-length relations of stimulated (active) and unstimulated (passive) 

 longitudinal flight muscle of bumble bee, Bombus. The muscle was stimulated to 

 maximum complete tetanus. The active tension curve was obtained by allowing the 

 muscle to shorten isotonically without a weight and then to build up tension at the 

 shorter length isometrically. The absence of the weight explains the difference be- 

 tween Fig. 9 and Fig. 10. The passive curve was obtained by stretching the unstimu- 

 lated muscle. 



An example of an isotonic response is illustrated in Fig. 10, recon- 

 structed from observations made on a number of preparations. The un- 

 stimulated muscle was loaded with 14 grams (c). On stimulation the 

 muscle shortened to b isotonically, and then began to oscillate with increas- 

 ing amplitude to a maximum c-c\ Upon the cessation of stimulation the 

 muscle lengthened and the oscillations decreased as shown by the envelope 

 c-a, c'-a. If the oscillations are prevented, the muscle shortens to d, a point 

 on the active tension-length curve. By jarring the preparation the oscilla- 

 tions again appear, the muscle lengthening and the amplitude increasing 



