Biomedical subjects
Publications and source records attributed to N A Morrison.
Genes involved in nodulation of both legumes and the nonlegume Parasponia sp., as well as nitrogenase genes, reside on a large plasmid in a fast-growing Rhizobium sp. from Lablab purpureus. This plasmid can be cured by incubation at elevated temperatures and can be mobilized by the P1 group plasmid RP1::Tn501.
The successful use of transposon mutagenesis in a slow-growing Rhizobium permitted the isolation of auxotrophic and symbiotically defective mutants. In these mutants, it was shown that different single-copy Tn5 insertions had occurred. Mutant phenotypes indicated that the control of nitrogenase activity in vitro and in planta is different.
Trees of the genus Albizia have frequently been confused with Acacia species. The genus Albizia has been recommended for more extensive arid zone development; its species are sources of tannins and gum exudates, which are not included in any of the regulatory lists of permitted food additives. Analytical data permitting their identification are therefore required to allow food law compliance to be monitored. This paper presents data which serve to characterize the gums from seven Albizia species, making a total of eleven Albizia species for which data are available. The presence of tannins, and high proportions of aluminium and heavy metals, indicates that gum importers and food processors must be vigilant to ensure that Albizia gums do not enter human food chains as adulterants or contaminants.
Combretum gums, readily available at low prices in East and West Africa, may be offered for sale as 'gum arabic'. Vigilance is necessary to detect such misrepresentations because Combretum gums differ greatly from gum arabic (Acacia senegal (L.) Willd.) in terms of quality, solution properties and value. Moreover, because there is no toxicological evidence for their safety in use, Combretum gums are not included in any of the international lists of permitted food additives. Food manufacturers and regulatory authorities therefore require data that characterize Combretum gums so that their use in foodstuffs can be prevented. This paper presents such data for the gums from a further six Combretum species. All of these have negative optical rotations similar to that of food grade gum arabic. It is no longer sufficient, therefore, to rely solely on an optical rotation measurement to confirm the identity of gum arabic. The additional analyses necessary to differentiate between Combretum gums and gum arabic are discussed.
The regulatory specifications for gum arabic (Acacia senegal) are superficial and inadequate to ensure that it is not adulterated with non-permitted gums from other botanical sources. Moreover, the existing specifications do not give the consumer the essential assurance, fundamental to food safety evaluation principles, that the nature and quality of gum arabic used in foodstuffs always conforms to that of the Test Article selected for the toxicological studies which justified the current status ('ADI not specified') of gum arabic as a permitted food additive. The availability of well-preserved gum arabic samples, collected between 1904 and 1939, has enabled invaluable data to be added to those derived from samples from the most recent crops. The resulting analytical data substantiate and greatly extend the quantitative information available previously for the chemical characterization of gum arabic for regulatory and trade purposes. The data confirm that good-quality commercial gum arabic was used previously as the Test Article. There is no evidence that the specific rotation of gum arabic has become significantly less negative in recent years.
Esotropia from chronic sixth nerve palsy or paresis usually requires surgery. Chemodenervation of the antagonist medial rectus muscle, while popular for the treatment of acute sixth nerve palsies and pareses, has not been used extensively for chronic cases. In this study, 22 patients with sixth nerve palsies or partially recovered palsies of greater than 5 months duration were treated with chemodenervation. The etiologies of the sixth nerve palsies were trauma (n = 7), tumor (n = 4), infection/inflammation (n = 3), nerve compression from aneurysm or increased intracranial pressure (n = 4), congenital (n = 1), ischemia (n = 2), and idiopathic (n = 1). The mean preinjection deviation was 41 prism diopters. A total of 38 injections were administered (mean, 1.7 per patient). Each patient received an injection of 2.5 to 7.5 units (mean, 4.1) of botulinum neurotoxin A to the ipsilateral medial rectus muscle. Treatment success was assessed 6 months after the last injection. A course of chemodenervation significantly improved the alignment of 9 of the 22 patients (41%). The mean postinjection deviation was 8 delta. Seven patients (32%) had single binocular vision in primary position restored. These patients had a mean horizontal binocular field of 70 degrees (range, 40 degrees to 100 degrees). Thirteen patients (59%) had only modest improvement and required surgery. The data suggest that injection of botulinum neurotoxin A is a useful treatment for some patients with chronic sixth nerve weakness. A course of chemodenervation therapy compares less favorably with transposition surgery with concomitant neurotoxin injection for the treatment of these difficult problems.