Mitogenic effect of sodium phenobarbital and rat liver arginase activity

Résumé Au cours de la régénération du foie normal des rats, on a constaté une augmentation — statistiquement significative — de l'activité arginasique dans la phase prémitotique. Chez des animaux traités par le phénobarbital, l'activité arginasique augmente encore davantage dans la phase prémitotique du foie régénéré.     

Centromere nature of the chromosomes ofRanatra (Heteroptera)

Zusammenfassung Histologisch-cytologische Untersuchungen zeigen, dass die Chromosomen vonRanatra monozentrisch sind. Der Befund steht im Gegensatz zu Ergebnissen anderer Autoren an andern Heteroptera-Arten, die polyzentrische Chromosomen haben. Die Natur des Centromers ist also bei verschiedenen Arten der Heteropteren verschieden.     

One electron transfer properties and phytotoxicity of a diquaternary salt from 2,2′:6′,2″-terpyridine

Zusammenfassung 2, 2:6, 2-Terpyridin gibt mit Aethylendibromid ein diquartäres Salz, das durch Reduktion mit Zink eine Radikalkation liefert. Es handelt sich um ein Redox-System und das Salz besitzt herbizide Wirksamkeit.     

Hypothalamic and cerebral cortical inhibitors of a melanocyte-stimulating substance secreted by the pars distalis of the frog pituitary gland

Zusammenfassung Nachweis, dass die pars distalis der Hypophyse des LeopardfroschesRana pipiens eine Melanozyten stimulierende Substanz enthält, die in vitro abgesondert wird. Wässerige Extrakte aus Hypothalamus und Kortex des Frosches hemmen die Ausscheidung der die Melanozyten stimulierenden Substanz in vitro.     

Der Eigenartige Einfluß Witelos auf die Entwicklung der Dioptrik

Summary Witelo's Perspectiva, which was printed three times in the sixteenth century, profoundly influenced the science of dioptrics until the Age of Newton. Above all, the optical authors were interested in the so-called Vitellian tables, which Witelo must have copied from the nearly forgotten optical Sermones of Claudius Ptolemy. Research work was often based on these tables. Thus Kepler relied on the Vitellian tables when he invented his law of refraction. Several later authors adopted Kepler's law, not always because they believed it to be true, but because they did not know of any better law. Also Harriot used the Vitellian tables until his own experiments convinced him that Witelo's angles were grossly inaccurate. Unfortunately Harriot kept his results and his sine law for himself and for a few friends. The sine law was not published until 1637, by Descartes, who gave an indirect proof of it. Although this proof consisted in the first correct calculation of both rainbows, accomplished by means of the sine law, the Jesuits Kircher (Ars Magna, 1646) and Schott (Magia Optica, 1656) did not mention the sine law. Marci (Thaumantias, 1648) did not know of it, and Fabri (Synopsis Opticæ, 1667) rejected it. It is true that the sine law was accepted by authors like Maignan (Perspectiva Horaria, 1648) and Grimaldi (Physico-Mathesis, 1665), but since they used the erroneous Vitellian angles for computing the refractive index, they discredited the sine law by inaccurate and even ludicrous results.That even experimental determinations might be unduly biased by the Vitellian angles is evident from the author's graphs of seventeenth century refractive angles. These graphs also show how difficult it was to measure such angles accurately, and how the Jesuit authors of the 1640's adapted their experimental angles to the traditional Vitellian ones. Witelo's famous angles, instead of furthering the progress of dioptrics, delayed it. Their disastrous influence may be traced for nearly thirty years after Descartes had published the correct law of refraction.

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Vorgelegt von C. Truesdell