248 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



tearing the membranes between the last two tarsal subsegments it is 

 simple to hold the terminal piece and pull out the long tendon that 

 extends from the pretarsal claws into the femur. This tendon may 

 be examined in lateral view as a whole mount, either in saline solu- 

 tion or after any desired treatment. 



For cross sections of the tendon, freshly dissected ones were cut 

 with a freezing microtome and transferred from the cold microtome 

 blade directly into 95-percent ethanol. 



Arthropodin was extracted from isolated cuticles of nearly mature 

 larvae of the fly Sarcophaga huUata. The larvae were eviscerated and 

 the cuticles swabbed in three changes of cold distilled water over a 

 period of 4 to 5 hours. The cuticles were then stored in 95-percent 

 ethanol at 5°C. for several months. Extraction was with hot distilled 

 water (90-95 °C.) for 6 hours. The filtrate was evaporated to dry- 

 ness and redissolved as needed. Artificial fibers were drawn manually 

 from a viscous mass as it was drying. 



Streaming birefringence was examined with a precision apparatus 

 built on the concentric cylinder principle. The apparatus was made 

 and is described by Kielley (1946). It is similar to the instrument 

 used by Dainty et al. (1944). Sensitivity was increased by use of a 

 Wratten green filter and dark-adapted eyes. 



Quantitative determination of the birefringence of chitin is easy. 

 One simply selects a tendon, purifies the chitin by extraction with 

 hot NaOH solutions or other chemicals, measures the path length 

 with a conventional ocular micrometer and the amplitude of bire- 

 fringence with an appropriate compensator. We used Kohler rotating 

 mica plates of i/io and 1/22 A maximum retardation and compen- 

 sated to half extinction, i.e., matched the brightness of the tendon to 

 the field (Bear and Schmitt, 1936). The magnitude of birefringence 

 of chitin is then given by 6/d, where ^ = 2wAsin B. B is the measured 

 rotation of the mica plate, A is the "center of gravity" of white light 

 (551 mix), and m is the maximum retardation of the mica plate 

 being used. 



Quantitative determination of the birefringence of arthropodin is 

 not so simple because good oriented alignment of molecules was not 

 achieved in our drawn fibers (to judge from the fact that values 

 calculated from them were much lower than values obtained by the 

 next method). Since streaming birefringence studies showed that 

 arthropodin exists in solution as considerably elongated particles, it 

 follows that thin sheets dried on glass should have good orientation 

 in the plane of the surface. However, orientation will be random 



