The morphology of physiological cell death and of necroses caused by treatment with various embryotoxic substances (cyclophosphamide, actinomycin D, vitamin A, vincristine, 6-aminonicotinamide, 6-mercaptopurine) and Mg deficiency were studied electron microscopically in rat and mouse embryos and fetuses. Three types of necroses were distinguished in control tissues.(1) Condensation and fragmentation of single cells undergoing phagocytosis, with lysosomal disintegration of the fragments in neighboring cells. (2) Primary formation of lysosomes in dying cells, with activation and subsequent destruction and phagocytosis of the fragments by neighboring cells. This type of cell death in most instances was found during destruction of organs and large cell units.(3) Disintegration of cells into fragments, which were optically no longer detectable, without involvement of the lysosomal system, e.g., in embryonic and epiphyseal cartilage before ossification. In cases of embryolethal toxic agents, e.g., Mg deficiency, cell necroses of large areas prevailed, which were characterized by typical pyknoses (rough, dense chromatin) and lack of lysosomes. In the case of teratogenic effects, however, substances that disturb replication, transcription, and translation (cyclophosphamide, actinomycin D, 6-mercaptopurine) caused an increase in the number of necroses of type 1. It can, therefore, be assumed that under these conditions similar processes take place in physiological and experimentally induced necroses. After administration of vitamin A, labilization of lysosomes and necroses of type 2 were observed.

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The surface of the cornea of rabbit eyes was studied under the scanning and transmission electron microscope, and was compared with the pathological changes which occurred after experimental UV irradiation. Both methods showed two types of cells: (1) cells rich in microvilli, containing an active karyoplasm and cytoplasm structure, and (2) smooth-surfaced cells with perhaps a few microvilli whose karyoplasm and cytoplasm are in a state of liquefication and whose membranes are defective. After U V irradiation, the microvilli were destroyed, and the second cell type was shed. The regeneration of the first cell type leads to a new formation of the microvilli from the centre of the cell, whereby tonque-like smooth processes can be seen at the periphery. These results support the thesis of the function-dependent formation of the microvilli and the age-dependent functional efficiency of the top layer of corneal, epithelial cells.

The superficial epithelial layer in the urinary bladder of adult rats was examined, in various states, using the transmission and scanning electron microscopes. A good agreement was obtained between the results of the two methods. When the urinary bladder is unexpanded, the superficial cells show marked bulges into the bladder lumen and the contacts between cells (mainly desmosomes) are displaced deep into the epithellium. The luminal surface is bizarrely bent and large parts of the membrane intrude into the cytoplasm, where they give the appearance of discoid and fusiform vesicles. Between neighboring cells, deep interdigitations are observed. In the scanning electron microscope, the surface of the epithelium appears cauliflower-like and has deep grooves, gullys and folds. When the bladder is expanded, the surface becomes smoother and the contacts between cells move to the surface. The stretched cells are angular in form (5-, 6- or 7-sided) and show great variations in surface area (150–500 μm²). The luminal cell membrane consists of an alternation of asymmetrical areas (120 Å thick and 0.2–0.4 μm in length) with normal sections which are 80 Å thick. In the scanning electron microscope, these thick areas appear as 4-, 5- or 6-sided plaques with a maximal diameter of 0.4 μm. The borders of the plaques are formed of portions of cell membrane which have a normal thickness and extrude as microcristae into the lumen. This produces a honeycomb appearance on the cell surface.

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