G Fischer – författare

Paleoceanographic proxies provide infonnation for reconstructions of the past, including climate changes, global and regional oceanography, and the cycles of biochemical components in the ocean. These prox­ ies are measurable descriptors for desired but unobservable environmental variables such as tempera­ ture, salinity, primary productivity, nutrient content, or surface-water carbon dioxide concentrations. The proxies are employed in a manner analogous to oceanographic methods. The water masses are first characterized according to their specific physical and chemical properties, and then related to particular assemblages of certain organisms or to particular element or isotope distributions. We have a long-standing series of proven proxies available. Marine microfossil assemblages, for instance, are employed to reconstruct surface-water temperatures. The calcareous shells of planktonic and benthic microorgan­ isms contain a wealth of paleoceanographic information in their isotopic and elemental compositions. Stable oxygen isotope measurements are used to detennine ice volume, and MglCa ratios are related to water temperatures, to cite a few examples. Organic material may also provide valuable infonnation, e. g. , about past productivity conditions. Studying the stable carbon isotope composition of bulk organic matter or individual marine organic components may provide a measure of past surface-water CO 2 conditions within the bounds of certain assumptions. Within the scope of paleoceanographic investigations, the existing proxies are continuously evolving and improving, while new proxies are being studied and developed. The methodology is improved by analysis of samples from the water column and surface sediments, and through laboratory experiments.

Until some years ago serum or crude tissue extracts were used pre­ dominantly or exclusively as media supplements for the cultivation of cells. However, during this time evidence accumulated that these sup­ plements could not provide in an optimal way most of the cultivated cells with all factors necessary for their survival, their prolifer­ ation and/or differentiation. Moreover, a variety of cells could not be cultivated at all under these conditions and often the composition of the cultures changed within rather short periods of time by overgrowth of initially present subpopulations of those cells which grow well in these supplements, as for example fibroblasts. Nevertheless, using these supplements (or fractions thereof), insight could be gained into some of the influences of serum or tissue extract constituents with re­ gard to survival, proliferation and differentiation of cells in cul­ ture. It became obvious from these experiments that serum or tissue extracts did not only supply cells with nutrients or vitamins (which are now constituents of all basic media), but also with hormones as well as growth-, differentiation-, and attachment-factors. In course of time experiments were performed in which serum enriched with hormones and other growth factors was used to successfully culti­ vate those cells which could not survive in serum-supplemented media alone. Under normal conditions in an organism, however, only a small population of cells has direct contact with serum.

Until some years ago serum or crude tissue extracts were used pre­ dominantly or exclusively as media supplements for the cultivation of cells. However, during this time evidence accumulated that these sup­ plements could not provide in an optimal way most of the cultivated cells with all factors necessary for their survival, their prolifer­ ation and/or differentiation. Moreover, a variety of cells could not be cultivated at all under these conditions and often the composition of the cultures changed within rather short periods of time by overgrowth of initially present subpopulations of those cells which grow well in these supplements, as for example fibroblasts. Nevertheless, using these supplements (or fractions thereof), insight could be gained into some of the influences of serum or tissue extract constituents with re­ gard to survival, proliferation and differentiation of cells in cul­ ture. It became obvious from these experiments that serum or tissue extracts did not only supply cells with nutrients or vitamins (which are now constituents of all basic media), but also with hormones as well as growth-, differentiation-, and attachment-factors. In course of time experiments were performed in which serum enriched with hormones and other growth factors was used to successfully culti­ vate those cells which could not survive in serum-supplemented media alone. Under normal conditions in an organism, however, only a small population of cells has direct contact with serum.

Dieser Buchtitel ist Teil des Digitalisierungsprojekts Springer Book Archives mit Publikationen, die seit den Anfängen des Verlags von 1842 erschienen sind. Der Verlag stellt mit diesem Archiv Quellen für die historische wie auch die disziplingeschichtliche Forschung zur Verfügung, die jeweils im historischen Kontext betrachtet werden müssen. Dieser Titel erschien in der Zeit vor 1945 und wird daher in seiner zeittypischen politisch-ideologischen Ausrichtung vom Verlag nicht beworben.