Twenty-two hysterectomy specimens were collected over a period of two decades in order to investigate the morphological sequence of menstrual desquamation and its consecutive remodeling of the endometrium. The technique used was described earlier by H. Ludwig and H. Metzger (1976). Scanning electron microscopy is the only way to illustrate and describe the microarchitecture of the endometrial surface. At the beginning of the menstrual bleeding, glandular stumps surviving the desquamation of the layer functionalis stick out from the debris at the top of the basal layer. Fibrin mesh formation, the liberation of lysosomes, and the emigration of white blood cells and macrophages, both being already present in the midluteal endometrial stroma, can be observed. They are interrelated with the clearance of the menstrual wound. Coincidentally with the process of desquamation the re-epithelization starts and takes the first four to six days of the normal cycle. The events are illustrated by selecting specimens of uteri from women with comparable data but from different days of the normal cycle. Surprisingly transitory excess formation of epithelial outgrows (micropolyps) are observed. They disappear later in the cycle, some might persist and form micropolyps, which will be the source of occasional intermenstrual bleeding--so far the polyps are vascularized. The endometrial surface is covered de novo by a lining surface epithelium at the sixth day. Ciliogenesis occurs within this epithelium. Other ciliated cells emanate from the glandular epithelium. In early stages of menstrual regeneration the growth pattern of the epithelial monolayer forming the lining surface in spiral traces according to their origination from the circle-structures of the endometrial glands. Before the incoming menstrual break-down small crevices, clefts or defects appear within the lining surface endometrium, a few white blood cells, enriched in the stroma around the vessels, might even reach the surface. The apical membranes of several non-ciliated cells exhibit rounded leaks, others show ruptures. It is the tissue break-down around the superficial endometrial vessels, what creates the onset of menstrual blood flow. In the very early preparations of the bleeding endometrium those opened capillary vessels could be identified.

The development of liver parenchyma starts from entodermal cells which grow out from the gut into the mesenchyma of the septum transversum. In the definitive organ this close association of epithelial cells (hepatocytes) and mesenchyma-derived nonparenchymal cells is maintained. The liver, and with it each hepatocyte, acts in two directions; the vascular poles of the hepatocytes serve in an ingestive sense, while at their biliary poles secretory functions are exerted. Hepatic microvascularization comprises two afferent vessels (arterial and portal terminal branches), the sinusoids and the terminal hepatic venule. Sinusoidal cells surround the capillaries but also have highly specialized functions with regard to filtration, phagocytosis, fat storage and defense. The autonomic innervation plays an important role in the regulation of metabolic functions. Above the cellular level the proper architecture of the liver parenchyma has been the object of controversial discussions for centuries. The concept of the liver lobule, the portal unit, the liver acinus and other structures are presented and discussed. Finally, the liver parenchyma is described as an irregular interdigitating system of regions related to the terminal blood vessels.

Studies on the endometrial cycle depend upon the precise dating of the cycle stage. In the present paper the generally applied method of vaginal smear was carefully verified through the measurement of the hormones relevant to the endometrial cycle. From rats predated through vaginal smear cytology, the hormone levels of estradiol-17-beta (E2) and progesterone (P), luteinizing hormone (LH), and follicle stimulating hormone (FSH) were measured. The values obtained were then compared to the standardized values of our reference curve. Animals with values that did not fit within the standard deviation of our reference curve were excluded from this investigation. Thus, for the first time exactly dated rat endometrial morphology was studied with electron microscopy. The morphology of the surface epithelium of rat endometrium from all four stages of the cycle is described in detail. In addition a semiquantitative morphometric analysis of the following parameters was performed: cell volume, nuclear volume, the volume density of secretory granules, digestive vacuoles, mitochondria, Golgi apparatus, rough endoplasmic reticulum, and lipid vacuoles as well as the size of lipid vacuoles. With the cellular content of lipid vacuoles and their diameter, it is possible to differentiate between proestrus/estrus and diestrus I/diestrus II, the latter possessing definitely more and larger lipid vacuoles. During estrus the greatest cytoplasmic volume develops. In addition to this, secretory granules are only present during estrus. Finally, diestrus I can be well differentiated from diestrus II, because diestrus I exhibits more digestive vacuoles and during diestrus II a high percentage of free ribosomes is present. On the basis of distinct morphological features, described in this paper, it is now clearly possible to distinguish between the four different cycle stages.

Digitization of glass slides and delivery of so-called virtual slides (VS) emulating a real microscope over the Internet have become reality due to recent improvements in technology. We have implemented a virtual microscope for instruction of medical students and for continuing medical education. Up to 30,000 images per slide are captured using a microscope with an automated stage. The images are post-processed and then served by a plain hypertext transfer protocol (http)-server. A virtual slide client (vMic) based on Macromedia's Flash MX, a highly accepted technology available on every modern Web browser, has been developed. All necessary virtual slide parameters are stored in an XML file together with the image. Evaluation of the courses by questionnaire indicated that most students and many but not all pathologists regard virtual slides as an adequate replacement for traditional slides. All our virtual slides are publicly accessible over the World Wide Web (WWW) at http://vmic.unibas.ch . Recently, several commercially available virtual slide acquisition systems (VSAS) have been developed that use various technologies to acquire and distribute virtual slides. These systems differ in speed, image quality, compatibility, viewer functionalities and price. This paper gives an overview of the factors to keep in mind when introducing virtual microscopy.

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