On the Biochemistry of Skin, and the Chemical Basis of Skin Swelling.
IN previous investigations by the authors [1924] it has been shown that the swelling of a fibrous tissue, such as skin, depends on both structural and chemical factors. The chemical factors considered were those due to variation in the external swelling medium. There remain those contributed by the skin itself. The influence of these is well shown by comparing the swelling of fresh goat skin with that of commercial sun-dried goat skin. The drying of the skin at a tropical temperature has caused a chemical change in its proteins which is made visible by the firm cementing together of the fibrils of the fibres. Skin is composed chiefly of proteins, though it contains in addition fats, sterols, and sterol esters. Rosenthal [1916] gives the following analysis of calf skin dried in vacuo at 55-60°.
Verlauf der Quellung bei Kollagen
ZusammenfassungDie Quellung von Kollagen wird vor allem von den nach außen wirksamen Überschußladungen bestimmt. Alle Maßnahmen zur einseitigen Hervorhebung der negativen oder positiven Ladungen wie: Entfernung vom I. P. oder einseitige Veränderung bzw. Blockierung polarer Gruppen sind deshalb quellungsauslösend.In der Nähe des I. P. führt die einheitliche Belegung mit Na⊕- oder K⊕-Ionen unter den hoch verdünnten Elektrolytlösungen oder unter Wasser zur zweidimensionalen innerkristallinen Quellung.Bei der Abschirmung der polaren Gruppen durch Gegenionen entstehen diffuse Doppelschichten, die eine Aufteilung der Fibrillen in einzelne Protofibrillen ermöglichen.Verdrängung der diffusen Doppelschichten durch Zusatz von Elektrolytlösungen höherer Konzentration bewirkt Entquellung der Fasern. Die Entquellung der Fibrillen, d. h. ihre Rekristallisation, ist aber wegen zu kurzer Assoziationszeiten nur unvollständig.Die Bindung zweiwertiger Kationen dürfte größtenteils äquimolar erfolgen und führt infolge Quervernetzung von Protofibrillen zu 80–100 Å dicken Längseinheiten. Quellung erfolgt erst zwischen diesen Vernetzungsprodukten.Die Einlagerung langkettiger anionenoder kationenaktiver Verbindungen verursacht infolge einer intrafibrillären Aufweitung das Eindringen von Quellungsflüssigkeit.
Reid on Hypotheses and the Ether; A Reassessment
In recent years historians of science have come to see that Thomas Reid’s Essays on the Intellectual Powers of Man had a profound impact on the development of British methodological thought in the late-eighteenth and early-nineteenth centuries. Larry Laudan has argued that Reid was “the first major British philosopher to take Newton’s opinions on induction, causality, and hypotheses seriously”; and that Reid was thereby instrumental in changing the character of British methodological discourse in the Enlightenment.(1) Geoffrey Cantor has examined in detail the influence of Reid’s critique of ether theories and hypotheses in the Essays on leading protagonists in the nineteenth-century debates surrounding the wave theory of light,(2) and Richard Olson has traced the origins of the scientific style of British physics in the Victorian period to the writings of Reid and other Common Sense philosophers. (3) As well as delineating Reid’s influence, Laudan, Cantor, and Olson have attempted to identify the problems to which he addressed himself in articulating his methodology, and they have analysed with some care the internal structure of his methodological views. Thanks to the work of these historians, therefore, we have a fairly comprehensive picture of Reid’s methodology and its fortunes in the nineteenth century.