Three crystalline modifications of isotactic polybutene-1 have been obtained from dilute solution in a variety of habits. These three crystalline modifications are: (a) tetragonal, (b) ``untwinned'' hexagonal, and (c) orthorhombic. The structure of the orthorhombic polymorph has not previously been reported. The basic morphology of all forms is the thin lamellar structure associated with polymer single crystals containing folded chains. A crystal-crystal transformation (from tetragonal to ``twinned'' hexagonal) was observed to occur when single crystals were allowed to stand at room temperature. This transformation involved a conformational change (from an 113 helix to a 31 helix), as well as the crystallographic one, but it did not involve a morphological change. No change in either morphology or crystallography occurred at room temperature in the orthorhombic or the ``untwinned'' hexagonal polymorphs, although both could be transformed completely into the tetragonal form if dried crystals were heated at 90°C for one hour. If allowed to stand at room temperature, the resulting tetragonal crystals transformed to the ``twinned'' hexagonal structure. The isotactic polybutene system thus constitutes an excellent case in which crystallographic, morphological, and conformational changes may be studied.

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The fine structure of acrylic fiber has been characterized using techniques based on gas adsorption, density, electron microscopy, and light microscoly. The techniques are complementary and have heen applied to acrylic fiber prepared under current commercial conditions. The existence of a fibril-void type of structure, with voids and fibrils of the order of 200 Å diameter, has been established for wet-spun fibers. This structure was shown to originate during coagulation and has been followed through stretching and collapsing. Dry-spun samples developed a similar structure, which becomes evident after the orientation step.

The formation of spherulites from concentrated solutions of polyacryloiiit,rile (PAN) has previously been reported in this Journal.' It was shown

The lingual epithelium is innervated by special sensory (taste) and general sensory (trigeminal) nerves that transmit information about chemical stimuli introduced into the mouth to the higher brain centers. Understanding the cellular mechanisms involved in eliciting responses from these nerves requires a detailed understanding of the contributions of both the paracellular and transcellular pathways. In this paper we focus on the contribution of these 2 pathways to the responses of salts containing sodium and various organic anions in the presence and absence of amiloride. Electrophysiological recordings from trigeminal nerves, chorda tympani nerves, and isolated lingual epithelia were combined with morphological studies investigating the location (and permeability) of tight junctions, the localization of amiloride-inhibitable channels, and Na-K-ATPase in taste and epithelial cells. Based on these measurements, we conclude that diffusion across tight junctions can modulate chorda tympani and trigeminal responses to sodium-containing salts and rationalize the enhancement of taste responses to saccharides by NaCl.