No abstract

In ~vo studies of Ehrlich ascites tumor cells during the first ,5 days of growth in peritoneal cavities of mice consisted of the following:1. Determination of growth curves by direct enumeration of cells. 2. Estimation of the duration of each phase of the mitotic cycle based on incidence of cells in different phases.3. Radioautographic studies to determine the proportion of cells in different phases of the mitotic cycle that incorporate tritiated thymidine during a single brief exposure to this precursor of DNA.4. Estimation of the rate of incorporation of tritiated thymidine at different times during the period of DNA synthesis by comparison of mean grain counts over nuclei in radioautographs at different times following exposure to tritiated thymidine.The assumptions underlying these experiments and our observations concerning the duration of the period of DNA synthesis and its relation to the mitotic cycle are discussed. It is concluded that DNA synthesis is continuous, occupying a period of 8.5 hours during the interphase and that the average rate of synthesis is approximately constant.

The structural features of the development of the bursa of Fabricius in white Leghorn chick embryos are depicted at carefully timed intervals during embryogenesis, with emphasis on the sequence of events between the ninth and twelfth days of incubation. The direction and character of the migration of lymphoid cell precursors and granulocytes from the intravascular space to intraepithelial sites, where the formation of the primitive lymphoepithelial nodule takes place, is demonstrated. The mechanism of the mode of migration of these cells through the stromal epithelial interface is described and illustrated with electron micrographs and their role in the development of the primitive lymphoid follicles is described and discussed.

A 75-year-old man with Staphylococcus aureus endocarditis in whom acute diffuse proliferative glomerulonephritis developed is described. The light- and electron-microscopic changes of the glomeruli in this case were identical to those of acute poststreptococcal glomerulonephritis. Immunofluorescence revealed deposition of immunoglobulins and complement in the glomeruli. In addition, bacterial antigenic material was demonstrated in the glomeruli by indirect immunofluorescence. These observations further support the hypothesis of an immune-complex pathogenesis in this form of glomerulonephritis.