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During the course of electron microscopic study of rapidly growing uninfected HeLa cells, it was found that numerous globoid bodies occurred in the cytoplasm. Reasons are given for suspecting that these structures are mitochondria.
1. A method is described for distinguishing the ribonucleoproteins of the nucleolus and parachromatin of ascitic tumor cells of the mouse. 2. In these cells the transfer of ribonucleoprotein from the nucleus to the cytoplasm can occur in two ways. (a) At the end of prophase the nucleolus separates from the chromosomes and nucleolar fragments are released into the cytoplasm. (b) During prophase the parachromatin is aggregated to form parachromatin bodies which are discharged into the cytoplasm, where they can be detected during metaphase, anaphase, and telophase. 3. A metachromatic form of RNA is demonstrable, and may be synthesized, in close relation to the chromosomes during prophase, metaphase, and anaphase. During telophase the distribution of metachromatic RNA changes, the chromatin loses its metachromasia, and intranuclear metachromatic parachromatin becomes evident.
Electron microscope studies of eight different sublines of Ehrlich ascites tumor cells which had not, as far as could be determined, come in contact with any known virus, revealed dense particles measuring approximately 55 to 70 mmicro in diameter, both within and attached to the wall of cytoplasmic vesicles identified as the endoplasmic reticulum. All tumor sublines contained significant numbers of particles and revealed no qualitative or quantitative differences in particle morphology or distribution. It is concluded that these structures are a constant morphological component of the Ehrlich ascites tumor and that they probably do not represent contaminating virus. Their morphology and distribution are described, and the possible interpretations of their significance are discussed.
The fibroblast-like tumour cells of Rous sarcomata have been studied in thin sections with the electron microscope. A description is given of the fine structure of the cells which includes some features not hitherto recorded. The tightly packed piles of smooth cisternae usually found only in the centrosome region have been observed, in individual Rous cells, in two separate areas of cytoplasm at opposite poles of the nucleus. Continuity between the perinuclear space and the lumen of rough surfaced cisternae of the endoplasmic reticulum has frequently been found; a similar continuity between the cisternae and the exterior of the cell has also been seen. In some cases, the cell membrane has been shown to have an unbroken connection with the outer nuclear membrane through continuity with the limiting membranes of elements of the endoplasmic reticulum. These findings are discussed.
The effects of x-irradiation have been quantitatively studied on single cells of a human cervical carcinoma (HeLa) under conditions such that 100 per cent of the unirradiated cells reproduce in isolation to form macroscopic colonies. This technique eliminates complexities due to interactions of members of large cell populations. Survival of single cells (defined as the ability to form a macroscopic colony within 15 days) yields a typical 2 hit curve when plotted against x-ray dose. The initial shoulder extends to about 75 r, after which a linear logarithmic survival rate is obtained, in which the dose needed to reduce survivors to 37 per cent is 96 r. This radiation sensitivity is tens to hundreds of times greater than that of any microorganism for which the equivalent function bas been studied. Evidence, though not proof, is presented that the lethal effect is due to a radiation-induced genetic defect which, however, cannot be a simple single gene inactivation. The locus of the action could be chromosomal. Beginning at doses of 100 r, or possibly earlier, growth-delaying effects of radiation are visible. Cells in which the ability to reproduce has been destroyed by doses below 800 r, can still multiply several times. At higher doses even a single cell division is precluded. A large proportion of the cells killed by radiation at any dose gives rise to one or more giant cells. These metabolize actively, grow to huge proportions but never reproduce under the experimental conditions employed. Methods of preparing large populations of giant cells are described. These giants are particularly susceptible to virus action. Some of the irradiated cells disappear from the plate, presumably by disintegration. This action of radiation is by far the least efficient, since even after 10,000 r, 5 to 10 per cent of the original cell inoculum is recoverable as giants.
A naturally occurring cutaneous fibroma of deer has proven to be experimentally transmissible in deer. The causative agent is a virus that is readily alterable through Berkefeld N candles and that survives in fibroma tissue for at least as long as 27 months in glycerol-saline at -20 degrees C. The experimentally produced deer fibroma has an incubation period of about 7 weeks, a very slow rate of growth, and a high regression rate.
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