Dense Vacuoles Research Articles

Candida albicans の Germ Tube 形成過程に関する電子顕微鏡的研究

The phenomenon of dimorphism exhibited by a number of species of pathogenic fungi has been well known. Candida albicans is one of the dimorphic pathogens which converts the yeast type cell into the germ tube-like filament (germ tube) in invading tissues. In order to study the pathogenicity and the mechanism of Candida albicans infection, the yeast type cells of synchronized growth were innoculated in proline medium to form the germ tubes in vitro, and the initial mechanism of the germ tube formation was investigated by electron microscope using various techniques. The results were as follows : 1. The initial appearance time and the rate of the germ tube formation are closely correlated with the cell size which may reflect cell maturation. The initial appearance in large cells is earlier than small cells and the rate of germ tube formation in the former is higer than in the latter. 2. The thickness of the germ tube wall is about a half of the yeast type cell's. The major part of the germ tube wall consists of the new layer, which is electron less dense, is formed between the inner layer and the cytoplasmic membrane of the mother cell. The electron dense outer layer of the mother cell grows over the germ tube as well, but the inner layer does not continue growing. 3. A great number of intramembranous particles and many invaginations are spreaded over the P. F. surface of the cytoplasmic membrane in freeze etching replica. The invaginations which exist on the germ tube are deformed and fewer than on the yeast type cell. The distribution of the particles becomes sparser toward the tip of the germ tube than that of the yeast type cell. 4. In the tip of the germ tube, the ER-derived vesicles become visible as membrane bounded circles with a diameter of about 100nm, containing some electron less dense granules. 5. With the commencement of germ tube formation, the membranous structures develop quickly, of which the elongating and dividing mitochondria and the lameller ER are found in the cytoplasm. 6. ATPase and acid phosphatase activities are demonstrated in the electron dense vacuoles in the cytochemical methods, which incorporate the phosphorus compounds. 7. As the yeast type cell evaginates, the electron dense vacuoles split and migrate toward the germ tube formation with vesicles, ER and mitochondria. During the development of germ tube, the vacuoles lose their electron density and become the empty structures.

The corpus luteum of the guinea pig. IV. Fine structure of macrophages during pregnancy and postpartum luteolysis, and the phagocytosis of luteal cells

Little information is available on the ultrastructure of macrophages in the corpus luteum or their importance in the regression of luteal tissue. In the present study, the fine structure of activated luteal macrophages during pregnancy and the postpartum period was examined by electron microscopy of guinea pig ovaries fixed by vascular perfusion. In these corpora lutea, macrophages can readily be distinguished from luteal cells. Activated macrophages typically display three prominent inclusions in their cytoplasm: (1) heterophagic vacuoles, (2) distinctive large dense inclusions, and (3) large and small electron-lucent vacuoles. In addition, they contain numerous smaller lysosome-like dense bodies. Activated macrophages in corpora lutea also characteristically show many surface protrusions, such as processes, folds or pseudopodia, which often occur in close contact with nearby luteal cells. Generally, nuclei of macrophages are irregular in shape and display a dense border of heterochromatin, thus differing from those of luteal cells. Macrophages seem to be most abundant in regressing corpora lutea, where they commonly display heterophagic vacuoles containing recognizable luteal cell fragments, evidence that these phagocytes ingest senescent luteal cells. The digestion of luteal cell components in heterophagic vacuoles presumably gives rise to the distinctive large dense inclusions typically seen in macrophages. The findings of this study indicate that macrophages play a central role in luteolysis by phagocytizing luteal cells or their remnants. They therefore appear to bring about the reduction in volume of the corpus luteum that occurs as this tissue regresses. These results taken together with those previously published (Paavola, '78) further indicate that breakdown of the corpus luteum during postpartum luteolysis in guinea pigs involves both autophagy and heterophagy.

Ultrastructural study of the platelets obtained from a idiopathic thrombocythemic patient associated with gingival and intramuscular hematoma, and with cerebral thrombosis

A sixty-year-old woman, who complained of headache and monoplegia of left upper extremity, was admitted to the Department of Internal Medicine of Tokai University Hospital in May, 1976.The spleen was palpable. The lymph nodes were not enlarged. Examination of the blood showed that platelet counts was 219×104 per mm3, white cell counts was 20, 800 per mm3. Bone marrow puncture revealed numerous megakaryocytes. On the hemostatic studies bleeding time, prothrombin time and partial thromboplastin time were prolonged. Ability of platelet adhesion decreased. Platelet aggregation studies showed the response to epinephrine and norepinephrine to be absent and that to ADP decreased. The ultrastructural features of platelets were reduction of α-granules, presence of bull'seye shaped dense granulations and vacuolization of ergastoplasmic reticulum and cytoplasm. The surface of platelet membrane was smooth and few projections from the cell membrane were observed.A mechanism of bleeding tendency in primary thrombocythemia was disccused, and it was suggested, on the basis of our findings that the cause of abnormality of the platelet function might have the relation with these abnormal ultrastructural findings.Diagnosis as idiopathic thrombocythemia, 2mg per day of busulfan was administered. Three months after busulfan therapy, she was in good condition with platelet count of 91×104 per mm3.

Observations on the morphology of the developing primate cornea: Epithelium, its innervation and anterior stroma

AbstractA survey is made of some ultrastructural features of the developing cornea of Macaca mulatta. The observations are confined to the anterior central area, starting with the lens vesicle stage and progressing through midgestation, when the morphologic characteristics of the cornea are fully established. Subepithelial filaments and some partially aggregated collagen fibrils are present in the earliest embryo and are of a size and appearance similar to those in the future vitreous cavity. Epithelial secretory activity points to, but does not prove direct contribution to the deposition of the acellular matrix components beneath it. No trace of a structured, orthogonal collagenous stroma can be visualized. The primitive endothelium forms prior to the fibroblast invasion of the distended filamentous matrix. Bowman's layer has undoubted epithelial contributions. Its aggregated collagen fibrils have approximately the same diameter as those of the anterior stroma. Intraepithelial appearance of single nerve fibers and fascicles takes place during the first trimester of gestation, as soon as the two continuous epithelial layers are formed. Terminal areas approach closely to the basal cell's nucleus, without touching it. The plasmalemma of the invaginating nerve fiber is surrounded by that of the epithelial cell in a mesaxon‐like manner, with occasional gap junctions uniting adjoining neural and epithelial cell membranes. The fetal neurites contain microtubules, some clear vesicles and dense vacuoles resembling those of mature monamine and non‐monamine neurons. Mitochondria are small and compact, their presence indicating a high rate of metabolic activity in the immature terminal area.

Cell death in ovarian chambers of Drosophila melanogaster

An ultrastructural analysis has been made of certain ovarian chambers undergoing abnormal development. The earliest morphological change in these chambers consists of the alteration of the nuclear material which is then followed by engulfment of portions of the nurse cell cytoplasm, including the nuclear fragments, into the overlying follicle cells. The continuation of this process leads to the progressive disappearance of nurse cells with the concomitant formation of huge dense vacuoles in the follicle layer. The morphological features described in the present investigation are similar to those found in other tissues and interpreted as leading to cell death. It is suggested that certain ovarian chambers undergo cell death as a result of the incapability of furthering their development. The role played by cell death in oogenesis is also discussed on the basis of the current literature.

Transmission and scanning electron microscopy of the human ceruminous apocrine gland. I. Secretory glandular cells.

The secretory portion of the apocrine sweat gland of the human external auditory meatus which is also called the ceruminous gland was observed by transmission and scanning electron microscopy. The secretory glandular cells contain a well developed smooth endoplasmic reticulum and Golgi apparatus. Cisternae of rough endoplasmic reticulum are often closely applied to large round mitochondria. These large mitochondria have no relationship to the secretory granules. Near the concave surface of the Golgi lamellae several tubules can be found. In these golgi-associated tubules a dark substance may accumulate to form specific large dense granules. Many less dense droplets or vacuoles may appear in these dark prosecretory granules and become liberated from their surface. Vacuoles formed in this manner then migrate to the apical cell surface and often discharge their contents into the gland lumen by the mechanism of exocytosis. Also, some of these vacuoles may be released into the lumen by the pinching off of small protrusions of cytoplasm, that is, they are released by the so-called apocrine secretory mechanism. Acid phosphatase activity was demonstrated not only in the dark prosecretory granules but also in clear vacuoles situated at the apical end of the cell and in the gland lumen. Such a histochemical finding may indicate that the secretory substance of the apocrine sweat gland may contain hydrolytic enzymes derived from lysosomes, which are the prosecretory granules of this gland, and these enzymes may play a role in dissolution and break down of the material extruded into the lumen by apocrine secretion. Apocrine secretory process of various sizes were observed on the luminal surface with the scanning electron microscope.

An ultrastructural comparison of the uptake and transport of horseradish peroxidase by the rat visceral yolk‐sac placenta during mid‐ and late gestation

AbstractHorseradish peroxidase was used to explore electron microscopically the uptake and transport of protein by the rat visceral yolk sac at 2 minutes, 6 hours, and 12 hours following a single intravenous injection into pregnant rats on day 12 and day 21.5 of gestation.On both days, the visceral endoderm absorbed peroxidase via micropinocytosis at 2 min postinjection, but not at the 6 and 12 hr intervals. At the latter two postinjection intervals on day 12, peroxidase was localized mainly at two sites, i.e., within intraepithelial supranuclear storage vacuoles, and within the vitelline endothelium deep to the visceral endoderm. On day 21.5 at 6 and 12 hr postinjection, peroxidase was localized in supranuclear storage vacuoles, though most of it was within tubular structures and small vacuoles in the paranuclear and infranuclear cytoplasm of the endoderm. Many dense vacuoles were in close anatomical relationship with the basal cell membrane. Deep to the endoderm a few macrophages were actively engulfing peroxidase, but reaction product was rarely found in the fenestrated vitelline endothelium.The results presented differ from the previous physiological and anatomical transport studies of the visceral yolk sac in that protein (peroxidase) transport was observed deep to the endoderm during both mid‐ and late gestation.

Capsella embryogenesis: The development of the free nuclear endosperm

The development of the free nuclear endosperm ofCapsella was studied using the electron microscope and histochemical procedures. The 2-nucleate and 4-nucleate endosperm contain many chloroplasts, mitochondria, dictyosomes, microbodies, polysomes, and an abundance of RER. There is a sharp decline in the starch and lipid reserves of the central cell during the first few divisions of the primary endosperm nucleus. Different developmental patterns occur in the micropylar and chalazal endosperms. Wall projections grow into the micropylar endosperm from the embryo sac wall and the suspensor wall. An unusual form of SER is continuous with the plasma membrane investing some of the suspensor wall projections of the heart-shaped embryo. The SER branches, forms clear and electron dense vacuoles and forms loops which encircle altered-appearing areas of cytoplasm. The micropylar endosperm of the heart-shaped embryo also contains many chloroplasts, mitochondria, dictyosomes, microbodies, polysomes, stacks of crystal-containing RER, and large nuclei which have many RER connections.

Granular cell tumors of the central nervous system.

This paper describes two cases of granular cell tumor, the first such tumors believed to have arisen in the central nervous system with the exception of those in the neurohypophysis. The tumor in one case arose in the cervical spinal leptomeninges and in the other was located in a cerebral hemisphere. The light and electron microscopic characteristics were indistinguishable from granular cell tumors (myoblastomas) reported in other body sites. Ultrastructurally two cell types could be distinguished. The predominant form (Type II) was characterized by abundant cytoplasm filled with dense bodies, multivesicular bodies and vacuoles. A second smaller cell (Type I) contained few of the above organelles. It is considered likely that these cell types are evolutionary stages of a single kind of a cell in which Type I is transformed into Type II. Various cells, including Schwann cells, have been proposed as giving rise to granular cell tumors. The occurrence of these neoplasms in the central nervous system lessens the likelihood of a Schwannian source in all instances. An origin from Schwann cells of perivascular nerves cannot be excluded. The possibility remains that neoplasms designated as granular cell tumors may have more than one cell of origin.

Ultrastructure and histochemistry of alumina in cortex

After intracortical injection of the epileptogenic compound alumina, positive histochemical reactions occur in the lesion border immediately and later in macrophages of the granuloma, blood vessels, and cortex. Perivascular alumina deposits may appear intraneuronal but are overlying instead. Moderately electronopaque alumina crystals ∼15 Å wide by 500 Å long increase their densities by adhering osmiophilic serum and cell products. Endocytosed crystals are seen in monocytes, fibroblasts, and astrocytes, but not in polymorphonuclear leukocytes or neurons. Macrophage secondary lysosomes, complex cytosegresomes, and dense and light vacuoles contain crystals at all stages from 1 day to 5 1 2 years after injection. Some crystals appear entangled in filaments and microtubules without definite limiting membranes. Intracellular alumina is assciated with increased cytoplasmic filaments, multivesicular bodies, lysosomes, free ribosomes, autophagosomes, and multiple vacuoles. Intracellular digestive processes may slowly degrade crystals into soluble compounds reflected by increased filaments in astrocytes and macrophages. These changes may indicate the sites of importance in the genesis of this type of epilepsy.

Quelques aspects ultrastructuraux de la substance blanche chez la souris quaking

The light microscopic study of the central nervous system of 30 Quaking and normal mice aged from 15 days to 8 months shows the abnormalities already described by Sidman et al. 42; moreover, there are many vacuoles in the whole white matter, and a glial proliferation without astrocytic reaction is present in the spinal cord. The ultrastructural study of the ventral funiculi of the cervical spinal cord in 20 other mice aged from 4 days to 5 months shows in the Quakings: (a) axomyelinic abnormalities: (1) a scarcity of the myelin sheaths and a striking diminution of their thickness; (2) a modification of the relation between axonal diameter and number of myelin lamellae; (3) the presence of astrocytic processes in the myelin sheaths; (4) distorted and disrupted myelin sheaths without visible signs of catabolism and some d degenerating axons; (5) numerous sheaths with ‘redundant’ myelin and several glial loops. (b) Glial abnormalities: (1) dense or round lamellar inclusions and vacuoles in the oligoglial processes; (2) many pleiomorphic inclusions in the perikarya of some glial cells; (3) numerous multivesiculated glial cells. The same inclusions, vacuoles and faulty myelination are visible in the basal ganglia and in the optic nerve. The relationship between the abnormalities, which predominate at myelination time in the myelin forming glial cells, and the modified composition of specific lipid components in myelin (especially in long chain fatty acids) remain to be established.

Ultrastructural morphology and histochemistry (acid phosphatase) of the cutaneous infiltration by polyvinylpyrrolidone.

SUMMARY.– Two new cases of skin infiltration by polyvinylpyrrolidone are reported. One had 2 types of macroscopic lesion: erythematous plaques, often with yellow pseudo-xanthoniatous papules in the centre, localized round the neckline and the front of the thorax, and small fibromata on the thighs and legs. The other patient had slightly indurated skin in the epigastric region. The ultrastructure of the histiocyte infiltration consisted of dense bodies and vacuoles with various structural variations. The authors stress the extremely generalized nature of this infiltration, affecting all the cell types of the skin, and the presence of intermediary forms linking the dense bodies to the vacuoles. Acid phosphatase activity is present in the dense bodies and certain intermediary vacuoles but absent from the large vacuoles. It is suggested that the dense bodies represent lysosomes with enzyme accumulation which then become loaded with polyvinylpyrrolidone, thus leading to the formation of large vacuoles with no enzyme activity. The well-developed Golgi apparatus in the histiocytes plays a part in the synthesis of lysosomal enzymes.

Observations on the epidermis of the miracidium and on the formation of the tegument of the sporocyst of Fasciola hepatica.

The relationship between the ciliated epidermal cells and the subepidermal layer of the miracidium of Fasciola hepatica has been described. Non-ciliated ridge-like extensions of the subepidermal layer separate the ciliated epidermal cells from each other. The sunken portions of the subepidermal layer, each containing a nucleus, lie below the outer body wall muscles of the miracidium and open into the ridge by narrow neck-like connexions. Elongate vesicles, which may be a source of stored plasma membrane similar to that which occurs in the transitional epithelium of other animals, fill most of the ridge. In addition, characteristic round electron dense granules are found in the ridge but the majority are found in the sunken portions of the subepidermal layer.The development and origins of the tegument of the sporocyst of F. hepatica have been described at the ultrastructural level. When the miracidium is in the process of penetrating the snail host, large vacuoles appear between the ciliated epidermal cells and the basal lamina which overlies the muscles of the body wall. These vacuoles have the effect of loosening the epidermal cells from the basal lamina of the body wall of the miracidium. Possible mechanisms involved in the formation of such vacuoles are suggested and discussed.During penetration of the snail the ciliated epidermal cells of the miracidium are lost; the ridge, a syncytial layer between the epidermal cells which is connected with the subepidermal layer, spreads over the basal lamina and exposed body wall muscles of the metamorphosing sporocyst to form the new outer covering of the sporocyst.Cytoplasm passes from the subtegumentary layer into the tegument during this stage of the development of the body wall of the sporocyst. Muscular contraction and microtubules may be involved in the outward movements of this cytoplasm. The nuclei of the subtegumentary layer remain below the muscles of the body wall.Twenty-four hours after penetration of the snail the outer plasma membrane of the tegument forms folds, which greatly increase the surface area.Sixty hours after penetration involutions between the folds, which may indicate pinocytosis, are present, and it is suggested that pinocytosis may play a role in food absorption.The fully formed tegument is a syncytial layer containing numerous electron dense granules, vacuoles, mitochondria and lipid droplets.The results on the formation of the tegument of the sporocyst have been discussed with reference to the controversy about the origins and terminology of the outer covering of the Platyhelminths.

Electron microscopical studies on the thyroid of a cyclostome, Lampetra japonica, during its upstream migration

Electron microscopical studies were made of the thyroid gland of an adult lamprey, Lampetra japonica, in the upstream migration period. The thyroid consists of many usual follicles containing the colloid in their lumina, and a large parafollicle without colloid. The paper concerns only the usual follicle. The follicle cells found in the usual follicle wall are classified into three types; 1. a non-ciliated taller cell, 2. a ciliated taller one, and 3. a non-ciliated cuboidal one. From their cytoplasmic fine structure, it is considered that all these cells are essentially identical and differences among them are due to their functional state. All these type cells are characterized by irregularly developed interdigitations and aggregates of tonofilaments throughout the cytoplasm, especially in the perinuclear region. Although the rough-surfaced endoplasmic reticulum and the Golgi apparatus are fairly well developed in the first and second type cells, the cisternae are not so large-vacuolated but flattened, and the cytoplasm is more compact as compared with that of the higher vertebrate. In the third type cell, the cytomembranes are poorly developed. Large dense inclusion-bodies consisting of heterogeneously dense materials, of lamellar structures, and of less dense vacuoles, which are found often in taller follicle cells, are also characteristic for the lamprey thyroid. The body which might be intimately related to the Golgi apparatus is considered to be a kind of lysosomes and it perhaps corresponds to the yellow pigment observed by light microscopy. In the apical part of the cytoplasm in taller cells, there are three kinds of granules or vesicles; numerous small vesicles considered to be derived from the Golgi apparatus, a few small dense granules which seem to originate from the Golgi region, and a few large less-dense granules. In the third type cell, the cytomembranes are not so well developed as those of the first and second type cells. The large heterogeneously dense bodies and the cytoplasmic granules are very few in number. Around the follicle of the lamprey thyroid, there are a dense basement membrane and a relatively compact connective tissue with few blood capillaries. Characteristic fat cells are found in the connective tissue.

Light and electron microscope studies of the redia ofParorchis acanthusNicoll

Young and old rediae ofParorchis acanthusNicoll, from the digestive gland and gonad ofNucella lapillus(L.) have been described. The young redia has an anterior collar-like fold and mid-ventral birth papilla the movements of which are controlled by a special arrangement of muscles. The birth papilla is ‘solid’ but in older rediae is replaced by a pore. The pharynx is of fairly uniform size irrespective of the size of the redia and the intestine, in the young redia, is relatively muchlarger than in the older redia which facts suggest that relatively more food may be absorbed by the mouth in the young stage. The redia cavity develops as a slit in the central cell mass. As it enlarges the intestine remains close to the dorsal wall and developing embryos are carried, among the cells, towards the surface dropping into the cavity, later, to complete their development. Up to fifty-five cercariae may be present in a redia. Simple nervous and excretory systems are present.The tegument consists of one layer; the surface bears numerous unusual branched microvilli. The syncytial protoplasm contains numerous electron dense mitochondria, vacuoles and granules. Half-desmosomes, not recorded for any other parasitic platyhelminth, occur fairly regularly on the lower limiting layer. Below the uninterrupted basement membrane are circular and longitudinal muscles and, lining the cavity, two or three layers of flattened cells containing numerous mitochondria, agranular and granular endoplasmic reticulum and Golgi complexes. Large lipid globules accumulate in the cells.It is suggested that, in the older redia, active transport of nutrient materials through the tegument may take place.

Morphology and function of the endoplasmic reticulum

Comparison with the findings in the cells of other plants and animals showed that the endoplasmic reticulum in the root apex ofFagopyrum has the same general character and function as in other biological objects, i.e. in secretory processes and especially in this case in the transport of the substances produced. Detailed studies of the morphology and activity of the endoplasmic reticulum showed some functional differences which are characteristic for this object. The endoplasmic reticulum participates apparently in the transport of the mass of known but functionally and nomenclatorically controversial formations which here are called dense bodies. Dense bodies exist inFagopyrum in a considerable amount as compared to other objects. Frequent contact of the dense bodies with the ends of the endoplasmic reticulum, contact with the endoplasmic retieulum passing through the plasmodesm, accumulation of the dense bodies along the cell wall and in proximal distance of the plasmodesms and intensive staining of some plasmodesms was observed. The dense vacuoles in this object represent dilated spaces of the endoplasmic reticulum which apparently have the function of reservoirs of the dense mass. The endoplasmic reticulum in the calyptra cells appears to participate in the formation of the cell walls. This object differs hereby from others, where the participation of the Golgi apparatus has been observed in this function.

The electron microscopic and classic Golgi apparatus

The relationship of the membrane structure, designated in electron microscopy as the Golgi apparatus, to the classic Golgi apparatus in the light microscope were studied withFagopyrum. Comparison of these structures in plant cells with the same or similar structures in animal cells led to the following conclusions: there exist two groups of formations, impregnable with osmium or silver, considered as the classic Golgi apparatus. The first group contains the active membrane structures. These are the dictyosomes and the anastomosing form of the electron microscopic Golgi apparatus. To this group belongs also the endoplasmatic reticulum, which in plant cells forms dense vacuoles, having the appearance of the classic Golgi apparatus, and in animal cells occasionally has a similar arrangement as the anastomosing form of the Golgi apparatus. The second group comprises formation containing reserve and secretion material, i.e. predominantly products of the activity of the electron microscopic Golgi apparatus and of the endoplasmic reticulum (matter of the dense vacuoles, lipochondria, secretory granula etc.). In the plant cells, especially ofFygopyrum, the dictyosomes contained in the structures of the first group are separated from the formations of a reserve character in the second group, formed in the lumen of the endoplasmic reticulum (dense vacuoles). The identity of the dictyosomes with the osmiophilic platelets, considered by some authors in the light microscope as the classic Golgi apparatus, has not been proved up to present, because of the one-sidedness of the methods used nowadays. WithFagopyrum no foundation has been observed for the assumed formation of net-form structures by grouping of the dictyosomes. Structures similar to the net-form of the classic Golgi apparatus in the animal cell form only dense vacuoles. On the basis of the differentiation of both types of formations in the plant cell, the foundations were laid for the characterization of the classic Golgi apparatus in the animal cell. The net-form of the classic Golgi apparatus in the animal cell is obviously not artificial, but reflects the ultrastructural arrangement of the electron microscopic Golgi apparatus or of the endoplasmic reticulum. The problem of the suitability and specification of the name Golgi apparatus in the animal and plant cell was also discussed. In contrast to the opinion of some authors, it does not appear useful to remove the name golgi apparatus, designating the dictyosomes and the anastomosing forms of the smooth membranes.

Klasický golgihe aparát a vakuoly

The dense vacuoles, considered to be the classic Golgi apparatus in the root meristem ofFagopyrum, were studied by the following methods: 1. Impregnation methods for the demonstration of the Golgi apparatus, 2. cytochemical methods, 3. electron microscopic methods in the light microscope and 4. the electron microscope. A comparison was made with the classic Golgi apparatus in animal cells in the light and electron microscope.

ELECTRON MICROSCOPY OF IN VITRO ENDOCYTOSIS OF T2 PHAGE BY CELLS FROM RABBIT PERITONEAL EXUDATE.

Macrophages from rabbit peritoneal exudate cells incubated in vitro with T(2) bacteriophage from 10 up to 120 minutes show phage particles adsorbed to cell membranes, in the process of being engulfed by means of rhopheocytosis, micropinocytosis, and phagocytosis, and localized within dense vacuoles, semi-dense vacuoles, and clear vacuoles of the cytoplasm. The electronmicrographs suggest that newly formed endocytic vacuoles containing phage particles fuse with one another and also fuse with dense bodies of the cytoplasm as they migrate towards the cell interior, thus yielding larger vacuoles of varying densities containing higher concentrations of phage. The polymorphonuclear cells present in a small proportion in the peritoneal exudate cells also endocytosed phage particles. The T(2) particles are found in large cytoplasmic vacuoles surrounded by an electron-opaque material presumably derived from cytoplasmic granules. No disintegration of T(2) phage within the macrophage following incubations up to 120 minutes could be demonstrated; however, disrupted phage particles were noted within cytoplasmic vacuoles of polymorphonuclear leucocytes after 15 minutes' incubation.

Electron microscopy of the slime moldPhysarum polycephalum

Electron micrographs of fixed sections of the plasmodium of the classic protoplasmic material,Physarum polycephalum, are presented. Numerous round nuclei having well-defined membranes and containing one to three dense nucleoli were especially prominent in the plasmodium. In the surrounding cytoplasm, many irregular membrane-limited bodies were evident, some containing tiny rod-like elements and others with inner structures resembling mitochondria. In addition, there can be seen many small dense granules plus various vacuoles and other inclusions.