Reaction of 6-aminopenicillanic acid with frequentin

Zusammenfassung 6-Aminopenizillansäure setzt sich mit Frequentin, einem Schimmelmetaboliten, unter gewissen Temperatur- und pH-Bedingungen um. Der entstandene Komplex stellt wahrscheinlich eine Tautomerenmischung aus Enamin und Enolimin dar, die beide durch Wasserstoffbrücken stabilisiert werden.     

Nouveau principe de stimulation électrique: L'excitation ambipolaire par courant alternatif,sinusoïdal pur,de fréquence moyenne

Summary Impulses of amplitude-modulated middle-frequency current (20 000 c.p.s.) stimulate nerve simultaneously at both poles. No polarity effect is observed, because no rectification occurs in the stimulation circuit if pure sine-wave middle-frequency current is employed. This principle is demonstrated by using bipolar longitudinal stimulation that, above threshold, elicits action currents, with latency difference corresponding to the distance between the stimulating electrodes. With supramaximum strength, maximum action currents are obtained at either pole, as is the case with ordinary cathodal stimuli of supramaximum strength applied to one pole or the other. Middle-frequency stimulation, therefore, has to be regarded asambipolar, i.e. does not depend on polarity. With second harmonic distortion, however, rectification occurs in the stimulation circuit and contamination by direct-current component ensues. Middle-frequency stimulation can be applied across nerve, since the excitatory effect does not apparently depend on longitudinal current flow. This method allows the action current to be recorded at the site of stimulation with minimum stimulus artefact.