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The chemical evidence for the enzymic activity of lysozyme will be discussed in detail by other speakers at this meeting, but in order to describe our crystallographic studies of the interactions between the enzyme and its substrates it is necessary to summarize briefly what was known about them at the beginning of our work. Simultaneously with his discovery of lysozyme Fleming (1922) discovered a Gram-positive species of bacteria, Micrococcus lysodeikticus , which is particularly susceptible to the action of the enzyme. It was not until much later, however, that Salton (1952) demonstrated that the substrate is located entirely within the bacterial cell wall and it is only very recently that its chemical constitution has been established. Valuable early experiments (for example, by Meyer, Palmer, Thomson & Khorazo 1936; Meyer, Hahnel & Steinberg 1946; and by Epstein & Chain 1940) showed that lysozyme releases N -acetyl-amino sugars from M. lysodeikticus , but the first indication of the type of linkage attacked by lysozyme came when Berger & Weiser (1957) showed that lysozyme also degrades chitin, the linear polymer of N -acetylghicosamine.

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LiBC ist eine neue, nur aus den leichten Elementen der Hauptgruppen bestehende Verbindung. Sie entsteht aus den Elementen in verschweißten Niobampullen bei 770 K und anschließendem kurzzeitigen Tempern bei 1 770 K in Form goldglänzender, hexagonaler Plättchen. Entsprechend Li+(BN)− bilden Bor und Kohlenstoff ebene Heterographitschichten vom Typ des isoelektronischen hexagonalen Bornitrids. Die Bereiche zwischen den Schichten sind durch Lithium vollständig aufgefüllt (P63/mmc; a = 275.2 pm; c = 705.8 pm; hP6; ZrBeSi‐Typ). Die Deformationsdichte der Valenzelektronen beweist für die BC‐Bindungen π‐Charakter und Polarisierung entsprechend (BC−). Nach chemischen und physikalischen Eigenschaften zeigt LiBC eine gewisse Phasenbreite x(Li) ≤ 1. Beim thermischen Abbau und bei chemischen Reaktionen entstehen bisher noch nicht charakterisierte BC‐Produkte. Die Oxidation von LiBC verläuft offenbar nach einem ähnlichen Mechanismus wie bei Graphit.

Ion currents of up to 30 mu A are readily obtained from liquid metal ion sources. The high electric field required to create the liquid cone from which emission occurs has given rise to the use of the term liquid metal field ion emission to describe the mechanism. Two candidate processes-field ionisation and field evaporation-are considered in the light of the available experimental data concerning the size of the cone apex, operating voltages etc. It is concluded that field ionisation or any other process requiring ionisation of thermally evaporated neutral atoms is unlikely to be the dominant process because of the absence of a heating mechanism capable of raising a sufficiently large area of the cone surface to the temperatures required. Field evaporation is, however, seen to be a possible mechanism provided an emitting feature of a few tens of angstroms is present. Alternatively, emission may be due to a moving asperity on the apex of a blunter emitting cone.

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