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The corneal potential was studied on the excised cornea mounted free from strain using the fine capillary electrode technique. The corneal potential obtained from the excised cornea was similar to that obtained from the enucleated whole eye. Concentration gradients were established across the endothelium. The potential differences were quite different from the diffusion potential. The endothelial barrier should be considered an ionic membrane. The intraocular pressure influenced slightly the corneal potential. The trans-corneal potential was a few mV, as long as the excised cornea was mounted free from strain; however, a large positive potential developed when it was clamped.

Die Kardinalvenen von Mauseembryonen der Tage 10 und 11 wurden im Bereich der Urnieren elektronenmikroskopisch untersucht. Diese Gefase sind von einem lockeren Mesenchym umgeben, das aus plumpen bipolaren oder fortsatzreichen Zellen besteht. In den Intercellularraumen ist eine beginnende Fibrillogenese nachzuweisen. Nach Anfarbung mit Rutheniumrot lassen sich hier Glykosaminoglykane darstellen. Die Venenwand selbst wird von einem einschichtigen, flachen Endothel gebildet. Neben typischen Endothelzellen kommen noch kubische, organellreiche Zellen ohne Fortsatze und Zellen mit plumpen, organellreichen Fortsatzen vor. Im Bereich des flachen Endothels treten intracellulare Lucken auf. Andere Lucken entstehen durch isolierte Einzelzellnekrosen im Endothelverband. Die durch beide Luckenarten eingeschrankte Permeabilitatsbarriere wird wahrscheinlich durch anliegende pericytenahnliche Mesenchymzellen aufrechterhalten. Weitere Befunde weisen auf einen Einbau von Mesenchymzellen in den Endothelverband hin. Es wird vermutet, das der Endothel-Mesenchymzellverband eine funktionelle Einheit bildet, die trotz starker Grosenveranderungen der Venen im Untersuchungszeitraum eine Aufrechterhaltung der Funktion ermoglicht.

Wear and tear degenerative patterns of the arterial system of the lower extremities have been studied in an age series. The intensity of these alterations has been correlated with the distribution of the atheromatous plaques and thrombosis as well as with the effective tension at various levels as calculated by Burton's formula. Evidence is presented for the concept that the lipids in atheromatous plaques arise as a product of these degenerative reactions within the vessel wall, rather than by diffusion from the circulation through the endothelial barrier.

Resume L'injection intraveineuse de cellules thyroidiennes dissociees, provenant de glandes neoplasiques, hyperplasiques et normales, chez la souris, met en evidence la capacite de ces divers types de cellules de penetrer l'endothelium vasculaire du poumon. Une telle penetration est demontree chez les animaux receveurs qui secretent un exces d'hormone thyreotrope. Les cellules thyroidiennes non neoplasiques semblent s'etablir dans le poumon suivant des processus semblables a ceux qui sont observes dans les metastases experimentales hematogenes de diverses cellules tumorales, c'est-a-dire: (a) par une proliferation intravasculaire initiale dans les capillaires ou les arterioles, proliferation suivie de la penetration de la paroi endotheliale et de l'extension dans l'espace alveolaire adjacent; (b) par la migration initiale des cellules thyroidiennes vers l'espace extravasculaire, et leur croissance ulterieure. Le fait que la penetration de l'endothelium vasculaire du poumon, par des cellules thyroidiennes normales, peut aussi s'observer en l'absence de stimulation par l'hormone thyreotrope est discute. A moins que le mode de penetration, mis en evidence dans ce travail, ne soit particulier aux cellules thyroidiennes, on peut mettre en doute l'hypothese selon laquelle la penetration de l'endothelium vasculaire du poumon, par des cellules cancereuses circulantes, serait liee a des capacites invasives propres aux cellules cancereuses.

The phenomena of fluid exchange in blood capillaries described by Starling's hypothesis are analyzed in terms of the properties of the endothelial barrier and the surrounding tissue. Two types of capillaries are defined: tube capillaries, where the rate of fluid exchange between intra- and extravascular space is determined by the capillary filtration coefficient, and tunnel capillaries, where the rate of exchange is determined by the hydraulic properties of the interstitium. The functional exchange properties of capillaries in mesentery, omentum, and cremaster muscle are shown to be those of tube capillaries. In hypothetical three-dimensional tissues whose capillaries and interstitium have the properties of mesentery, the functional aspects of fluid exchange can be explained by either model. It is also shown that in tissues whose capillaries are of the tunnel type exchange is strongly influenced by the capillary spacing. These results provide a basis of determining the relative importance of the endothelial barrier versus the surrounding medium as factors that govern fluid exchange.

The fine structure of the sheep hepatic sinusoid has been examined. Unlike that of most previously studied mammals, the sheep sinusoid has a continuous endothelial lining and a distinct basal lamina. Another unusual feature of the sheep sinusoidal endothelium is the presence of fenestrae closed by thin, single-layered diaphragms. Between the basal lamina and the hepatic parenchyma, processes of perivascular connective tissue cells are seen in unusual abundance. Particles consistent in size with very low density lipoproteins are found on both sides of the basal lamina, but the mechanism of transport of these particles across the endothelial barrier is unknown.

Repeated injections of angiographic contrast media led to disruption of the endothelial barrier of the cerebral parenchymal capillaries (blood-brain barrier) experimentally by (a) promoting pinocytosis and (b) opening the tight junctions which exist between the endothelial cells.Two mechanisms appear to be involved in this process. The hyperosmolar quality of the contrast media is responsible for the increased pinocytosis, while the chemical nature of the contrast agents used (Hypaque 50, and Conray 60), results in opening of the tight junctions.

Human donor corneas, stored at 4C or cryopreserved, were subjected to in-vitro perfusion, pachometry, and endothelial permeability determinations. The endothelial barrier mechanism and metabolic pump mechanism of the corneal dehydration system were thereby assessed at various durations of storage. Estimates of normal human endothelial permeability to urea and sucrose are presented.