A mechanism of mitosis is described based on the data, collated as a result of studies of mitoses in vivo in Tradescantia stamen hair cells. In the analysis of the mitotic processes attention was paid not only to the microscopic but also to the submicroscopic organization of the mitotic elements, and upon their continuous physico-chemical changes all the mitotic processes were discussed. (1) To explain the fundamental problem of the mitotic mechanism the writer has discussed and compared the different views, proposed as a consequence of the investigations of the achromatic figure in vivo and in fixed preparations, and demonstrated that the disappearance of the nuclear membrane in the metaphase is an artifact caused by fixatives. In the living state of the mitotic cell the nuclear membrane is maintained continuously from the prophase up to the beginning of the telophase, changing its shape and also its structure. (2) As a result of these studies and taken together with a consideration of the submicroscopic structure of the polar cap stage, the intranuclear origin of the spindle substances, the developmental processes of the spindle fibers, and the chromosome movement in the prometaphase are ascribed to the bipolar force of the mitotic cell and the conversion of the molecular configuration of the nucleoproteins. (3) The fibrillar structure of the spindle body is divided into two kinds. One kind constitutes the ground fibrillar structure and takes no immediate part in the chromosome movement in the anaphase. The other kind is the chromosomal fiber or the traction fiber which grows along the ground fibrills from the kinetochore to the spindle poles. This fiber may be a bundle made up of the ground fibrills enclosed by the kinetochore substances. The traction fibers may become short by the dissolution of their kinetochore substances and by the disintegration of their molecular fibrills: these changes occur successively in the poles of the anaphase spindle. (4) The chromosome movement in the anaphase is described as a result of the shortening of the traction fibers, which act as pulling forces upon the kinetochore of the daughter chromosomes. (5) The substantial continuity between spindle body and the phragmoplast, the process for reconstructio i of the metabolic nuclei from the daughter chromosomes, the development of the cell-plate, of the cell-wall, and of the neclear membrane of the daughter nuclei are demonstrated experimentally and interpreted submicroscopically. (6) In the theoretical interpretation of the mitotic mechanism the following factors should be considered: (a) the reversible denaturation of the nucleoproteins:-mainly the conversion of the molecular configuration from corpuscular to fibrillar by the unfolding of the polypeptide chains, and vice versa, (b) the bipolar force in the mitotic cells, (c) the existence of the spindle body delimited by a surface film, (d) the action of the kinetochore substances, (e) the shortening of the traction fibers and (f) the swelling of the atractoplasm.
In the cryptorchid testes of white rats which were artificially confined in the abdominal cavity, degeneration phenomena of germ cells were cytologically investigated. As cytological phenomena taking place in association with the degeneration, the following abnormalities were observed: stickiness and coalescence of chromosomes, swelling of chromosomes, deformation of chromosomes into bodies of round shape, chromosome bridges at anaphase, scattering or displacement of chromosomes at metaphase, non-disjunction and lagging of chromosomes at anaphase, irregular distribution of chromosomes at anaphase, varying numbers of chromosomes, formation of bi- and multi-nucleate cells, and uni- and multi-polar mitoses. A tentative conclusion was drawn on the cause of these mitotic abnormalities that a change in normal water distribution in the cell may be taken as a favourable basis of explaining the question.
PMCs of T. kamtschaticum were irradiated at their resting stage, and the following results were obtained. 1) The irradiation leads to the production of both “chromosome” and “chromatid” breaks. 2) The reunion of broken ends occurs between two broken ends as well as between a broken end and a normal end. 3) Broken ends do not often reunite. These free broken ends of chromatids reveal themselves in the next division (that is, in the first pollen mitosis) as paired chromatids which are bridged together at their broken ends. 4) The frequency breaks per chromosome is proportional to the length of whole chromosomes. 5) The frequency of bridges and loops which appear at the first anaphase indicated the ratio of 2 bridges: 1 loop within intra-bivalent aberrations and the ratio of 1:1 in inter-bivalent aberrations. These ratio verify that the mode of disjunction of the paired kinetochores of a bivalent follows the principles of the neo-two plane theory.
Against the current inversion theory on the origin of chromatid bridges and fragments at meiotic anaphases, the present study introduces an alternative interpretation. It implies a possibility of recombinations of chromatids at the chiasma region as the consequence of normal crossing-over (Fig. E). At this moment the random reunion of chromatids is subjected to certain limitation by the cleavage of chromosome matrix. Thus the resultant configurations are three types, X, Y and O, as represented by Fig. C. The former two types relate to the formation of bridge and fragment at anaphases; the last implies the dissolution of the chiasma. If these three types are subjected to such a series of relationship as the present work has shown, this will be not only at variance with the inversion theory, but also strongly support my theory of crossing-over.
1. In a series of experiments on starvation and subsequent alimentation, changes of mitochondria of rat liver cells were examined in relation to the types of hepatic cytoplasm as regards the distribution of ribonucleic acid and some other properties of the liver. 2. At the agonal stage resulting from starvation, mitochondria were found always to be greatly enlarged in hepatic cells which had undergone condsiderable diminution in size and in which the cytoplasmic ribonuleic acid had been remarkably reduced. This is accompanied by only slight decrease of specific gravity of the liver tissue, which suggest that this type of mitochondrial or cytochondrial enlargement is not caused by a simple osmotic swelling. 3. The alteration of mitochondria and cytochondria in the course of starvation was considered under the light of a hypothesis that mitochondria fixed in ordinary fixatives take the figure to be identified as cytochondria. 4. A remarkable change of the free amino acid pattern obtained preliminarily by paper chromatography was found to accompany the premortal enlargement of mitochondria caused by starvation. The writer expresses his hearty thanks to Dr. Y. Saito, late Miss H. Kawamata, and Mr. T. E. Y ukimura, Medico-Biological Institute, Minophagen Pharmaceutical Co., for their valuable assistance and criticisms unsparingly given him.
The origin and development of the vacuolar system and the effect of hydrogen-ion concentration on the accumulation of neutral red in the vacuoles of the vegetative mycelium of Achlya sp., Brevilegnia gracilis, Isoachlya anisospora var. indica and Saprolegnia monoica has been studied. The vacuoles, which are small rounded or oval shaped at the tips of the hyphae, and the vacuolar canal are seen to be composed of a colourless homogeneous solution and appear optically empty under the ultramicroscope. The vacuolar system becomes more clear with vital dyes. The vacuoles are seen arising de novo at the tips of young hyphae. These small vacuoles fuse to form a network or a chain of round or ellipsoidal vacuoles which in turn fuse again to give rise to a continuous vacuolar canal. At times the vacuolar canal of a parent hypha is seen passing into the daughter hyphae. No metachromatic corpuscles are found in the hyphae of the fungi studied. When grown in peptone solution with neutral red, numerous vacuolar precipitates, pre-existing corpuscles and sphaerocrystals are seen in the vacuolar canal. The colour and the vacuolar precipitates in the vacuolar canal are retained for a longer time in the hyphae grown on a poor medium. Rapid growth on a rich medium causes the excretion of the dye. Neutral red accumulates in the vacuoles at pH values between 6 and 8.5. In the case of Brevilegnia gracilis it accumulates at pH between 6 and 8 only. In conclusion I wish to express my warmest gratitude to Dr. R. K. Saksena for his kind guidance and encouragement throughout the course of the study. I am grateful to Professor S. R. Bose for his help in many ways and to Dr. F. M. L. Sheffield for kindly going through the manuscript.
The effect of various chemicals and temperature on the structure of mitochondria found in the vegetative mycelium of Achlya sp., Brevilegnia gracilis, Isoachlya anisospora var. indica and Saprolegnia monoica has been studied. The mitochondria are seen as long filamentous and slender bodies of varying length lying mostly parallel to the longitudinal axis and constantly moving under the influence of the cytoplasmic currents. At the tips they are granular in shape and are seen in the process of elongation just behind it. They are invisible under the ultramicroscope. Janus green Hocht B and dahlia violet stain them, transforming them into vesicles. It is not possible to stain them intravitally with these dyes. The vacuolar system and the mitochondria are stained simultaneously by using a mixture of neutral red and Janus green. They are able to resist the temperature of 55°C which does not destroy them. Sulphuric acid (1 percent) and absolute alcohol destroy them: hydrochloric acid (1 percent), sodium hydroxide (1 percent), glacial acetic acid, benzene, ether and chloroform modify their shape: nitric acid (1 per cent) and acetic acid (1 per cent) produce corrosions on their surface but picric acid does not affect them. Of all the fixatives Helly's liquid and formol-sublimate gave good results. Liquid of Lenhossek (containing alcohol and acetic acid) and Bouin's fluids (containing acetic acid and picric acid) do not produce any marked change. Preparations treated with Kolatchev's technique show well preserved mitochondria together with nuclei and vacuolar precipitates, all of which become black. It is suggested that there is nothing like ‘Golgi-bodies’ in the fungi. I wish to express my appreciation to Dr. R. K. Saksena for his guidance and helpful suggestions and my thanks are due to Professor S. R. Bose for examining my preparations. I am grateful to Dr. F. M. L. Sheffield for kindly going through the manuscript.