Small Rim Research Articles

Benign Cerebellar Astrocytomas of Childhood

Benign cerebellar astrocytomas of childhood are potentially surgically curable lesions. Histologically, these neoplasms can be divided into pilocytic and diffuse astrocytomas. Whether there is a difference in the recurrence rate between these two tumor types after a surgical resection is not clear. In addition, the role of immediate postoperative imaging in predicting a recurrence has not been established. To answer these questions, we have reviewed the charts of 23 patients with benign cerebellar astrocytomas treated at Childrens Hospital of Los Angeles over a 10-year period (1977-1987). Of the 23 tumors, 15 were pilocytic and 8 were diffuse. All patients underwent an attempted gross total surgical removal of the tumor, and all patients had a postoperative computed tomographic (CT) scan with and without intravenously administered contrast material performed within 72 hours of the operation. Based on the postoperative CT scan, 12 patients had residual tumors. Seven of the subtotally resected tumors were pilocytic (7 of 15), and 5 were diffuse (5 of 8). Interestingly, the surgeon believed that a gross total resection had been obtained in 9 of these patients. There have been 4 recurrences in these 23 patients, with a mean follow-up of 4.9 years. All recurrences were in patients with subtotal resections. Of the 11 patients with a total resection of the tumor, 7 developed a small rim of enhancement on subsequent scans an average of 5 months after the operation.(ABSTRACT TRUNCATED AT 250 WORDS)

天北・羽幌地域の石油地質 深部構造特性と炭化水素ポテンシャル

The thick Cretaceous-Tertiary sediments which cover the Tenpoku and Haboro area, the northern part of Hokkaido, is believed to possess substantial hydrocarbon potential. More than seventy anticlinal structures have been recognized in this area, but to date only eight wells have penetrated the Paleogene section while four have drilled to Cretaceous sediments.Four types of anticlinal structures are recognized as interpreted from well data and seismic profiles. The Kitakawaguchi feature represents the first type of anticline. Two wells have been drilled on this structure and seismic profiles are available. A gentle antiform exists as the Paleogene section drapes across thrust-faulted Cretaceous sediments. A more pronounced Neogene anticline is superimposed upon the pre-existing structure. The later structure was formed by flowage of Miocene shales and associated thrust-faulting. The Miocene shales exhibit abnormally high pressure and steep dips. Small rim synclines commonly exist on the flanks of this type of structure.The Uttsu Anticline illustrates the second type of anticlinal feature. The MITI Enbetsu well was drilled to test this structure. The anticline was formed by deep-seated vertical thrust-faulting which affected Paleogene and Cretaceous strata. The formation of the anticline produced an important effect on Tertiary sedimentation. Similar features are thought to exist along the Horonobe and Magaribuchi-Toyotomi fault systems.The Rikibiru structure is an example of the third type of anticline and is located in the southern part of the study area. The MITI Rumoi was drilled on the western flank of the feature. Dipmeter logs indicate that this deep Cretaceous structure is quite huge and broad with gently dipping flanks. The thick sequences of coarse-grained Miocene sediments deposited in this area contrast with the predominantly shaly strata seen to the north. The formation of the Rikibiru Anticline is thought to have formed due to loading of the thick Miocene section. Shale flowage did not occur in this area due to the lack of thick shale sequences.The Maruyama Anticline illustrates the fourth type of anticlinal structure. No wells have been drilled to date on this type of feature. These anticlines are broad and gentle-dipping and are surrounded by rim synclines similar to those exhibited by the first anticline type.Growing mechanism, timing and distribution of each type of anticline are discussed with the view of petroleum geology.

Immunohistochemical localization of polypeptide hormones in pancreatic endocrine cells of a dipnoan fish, Protopterus aethiopicus

Light microscopical immunohistochemistry was used to demonstrate the regulatory peptides present in the endocrine pancreas of Protopterus aethiopicus. The peptides studied included insulin, glucagon, pancreatic polypeptide and somatostatin. The results showed that the 4 regulatory peptides commonly detected in the mammalian endocrine pancreas were immunologically discernible in this dipnoan fish. Large amounts of insulin-immunoreactive cells, in the centre of the pancreatic islets, were surrounded by a small rim of glucagon-or pancreatic polypeptide-immunoreactive cells. In addition, adjacent sections stained with anti-glucagon and anti-pancreatic polypeptide revealed that these hormones could be found in the same cells. Somatostatin-positive cells were scattered throughout the islets. Their processes were seen to contact many different endocrine pancreatic cells, suggesting that the somatostatin-immunoreactive cells control the functions of other endocrine pancreatic cells.

Posterior Labral Tear as a Block to Reduction in an Anterior Hip Dislocation

The patient presented with an anterior dislocation of the hip that could not be centrically reduced by closed methods. Computed tomographic imaging after trial reduction revealed a posterior fragment that was limiting reduction. At the time of open reduction, a large posterior labral tear with a small avulsed posterior acetabular rim of bone was found to be blocking the reduction.

Gadolinium‐DTPA Enhanced Magnetic Resonance Imaging in Acoustic Neuroma Diagnosis and Management

Gadolinium-DTPA (Gd-DTPA) is a paramagnetic contrast agent that increases the intensity of acoustic neuromas (AN) on T1-weighted magnetic resonance imaging (MRI) scans. Over a 9-month period we have reviewed Gd-DTPA-enhanced MRI scans on 32 consecutive cases (35 tumors) involving the internal auditory canal (IAC) and cerebellopontine angle (CPA). The majority of patients (84%) were imaged on latest generation 1.5 Tesla scanners. Every tumor studied showed marked enhancement after Gd-DTPA administration. This improved contrast permitted identification of three small tumors that were not evident on unenhanced scans. Gd-DTPA appears to be particularly useful in the evaluation of recurrent or residual AN. In three patients with known residual tumor after planned subtotal excisions, the remaining tumor could only be differentiated from surrounding scar, cerebral spinal fluid (CSF), and brain parenchyma after contrast enhancement. In one of these, a small rim of tumor capsule left on the facial nerve was evident only on Gd-DTPA-enhanced T1 images. Gd-DTPA also provides a more reliable estimate of the depth of tumor penetration in the IAC. This information is useful in selecting candidates suitable for a hearing conservation approach.

Primary myxoma of the posterior fossa

A rare case of primary intracranial myxoma of the posterior fossa is described in a 32-year old woman. The patient presented with a history of headaches, disequilibrium, nausea and abnormal vision for several months. Computed tomography (CT) showed a well-demarcated hypodense mass. After contrast administration the mass appeared as an inhomogeneously enhancing lesion surrounded by a small rim of edema. The mass was surgically excised with histological examination revealing a true myxoma. Echocardiography revealed no evidence of a cardiac myxoma. The CT appearance of other case reports of non-cardiac myxomas in the literature is reviewed.

Large animal model of left ventricular aneurysm

In 28 Dorsett sheep, ligation of the distal homonymous (equivalent to human left anterior descending) and second diagonal coronary arteries produced a constant transmural infarct of 22.9% ± 2.5% (mean ± standard deviation) of the left ventricular mass. Serial left ventriculograms showed that within four hours the infarct segment expands, wall thickness decreases, and aceurysmal dilalation occurs and progresses over the next 60 days in all sheep. Epicardial ventricular point references indicated that adjacent noninfarcted myocardium participates in the formation of the aneurysm. Anatomy of the coronary vasculature was studied in 22 excised sheep hearts. In sheep, coronary arterial anatomy is remarkably constant. The left coronary artery provides all of the blood supply to the left ventricle and septum and only a small rim of both the anterior and posterior right ventricles. Crdiac veins from the left ventricle drain into the coronary sinus, which also receives the left azygos vein. Right ventricular veins drain separately. The essentially separate coronary circulations to the two ventricles, the paucity of coronary collateral circulation, and the consistent evolution of left ventricular infants into aneurysms are important advantages of the ovine model for both metabolic and ventricular maechanical studies of acute myocardial infarction and left ventricular aneurysm.

Giant iatrogenic splenic pseudocyst

Partial splenic arterial embolization was used to treat hypersplenism in a 10-year-old boy with portal hypertension secondary to congenital hepatic fibrosis. After embolization the spleen remained enlarged, but the boy's platelet count increased and his variceal bleeding ceased. One month later, he returned with vomiting and an abdominal mass. Computed tomography showed a large cyst of the spleen with a small rim of residual splenic tissue. Percutaneous drainage with ultrasound guidance yielded 2,800 mL of brown fluid. Wedge-shaped infarctions are described early after splenic embolization, and these areas eventually fibrose and contract. In this case, the embolization resulted in splenic necrosis and liquefaction with pseudocyst formation. This unusual complication was effectively treated without surgery.

Changes in right ventricular relaxation during acute anterior myocardial infarction in pigs.

To determine the effect of an anteroseptal myocardial infarction on right ventricular systolic and diastolic function, we studied 12 pigs before and 1 h after left anterior descending coronary artery occlusion. Total arterial occlusion was achieved by the percutaneous, transcatheter placement of a 1 mm Teflon plug into the mid portion of the artery. The resulting infarction involved 28 (SEM 3)% of the left ventricular wall, in the anterior and septal regions. A small rim of the right ventricular free wall adjacent to the septum and the right ventricular apex were also affected. End diastolic pressures in both ventricles rose significantly: left ventricular from 12(1) to 20(2) mm Hg and right ventricular from 8(1) to 10(1) mm Hg. Right ventricular peak systolic pressure increased from 29(2) to 35(2) mm Hg while left ventricular peak systolic pressure did not change. One hour after infarction the half time of isovolumic relaxation of the right ventricle was prolonged from 6.9(0.5) to 8.7(0.4) ms. Ejection fraction in both ventricles was depressed: from 46(1) to 34(2)% in the right ventricle and from 69(3) to 49(3) in the left ventricle. There was no change in either right or left ventricular dP/dt. These data suggest that right ventricular systolic and diastolic dysfunction occurs as the result of an anteroseptal myocardial infarction in pigs.

Functional morphology of the ommatidia in the compound eye of the moth, Antheraea polyphemus (Insecta, Saturniidae).

The fine structure of the superposition eye of the Saturniid moth Antheraea polyphemus Cramer was investigated by electron microscopy. Each of the approximately 10,000 ommatidia consists of the same structural components, but regarding the arrangement of the ommatidia and the rhabdom structure therein, two regions of the eye have to be distinguished. In a small dorsal rim area, the ommatidia are characterized by rectangularly shaped rhabdoms containing parallel microvilli arranged in groups that are oriented perpendicular to each other. In all other ommatidia, the proximal parts of the rhabdoms show radially arranged microvilli, whereas the distal parts may reveal different patterns, frequently with microvilli in two directions or sometimes even in one direction. Moreover, the microvilli of all distal cells are arranged in parallel to meridians of the eyes. By virtue of these structural features the eyes should enable this moth not only discrimination of the plane of polarized light but also skylight-orientation via the polarization pattern, depending on moon position. The receptor cells exhibit only small alterations during daylight within the natural diurnal cycle. However, under illumination with different monochromatic lights of physiological intensity, receptor cells can be unbalanced: Changes in ultrastructure of the rhabdomeres and the cytoplasm of such cells are evident. The effects are different in the daytime and at night. These findings are discussed in relation to the breakdown and regeneration of microvilli and the influence of the diurnal cycle. They are compared with results on photoreceptor membrane turnover in eyes of other arthropod species.

Hamatometacarpal fracture-dislocation: Classification and treatment

Seventeen male patients with a fourth metacarpal fracture and fifth carpometacarpal joint injury were treated. Distinct patterns of injury were recognized and in each case fell into one of three categories. Type IA lesions were characterized by subluxation or dislocation of the fifth carpometacarpal joint without hamate avulsion fracture. Type IB lesions were identical to type IA lesions except for the appearance of a small dorsal rim hamate avulsion fracture. Type II lesions were distinguished by subluxation or dislocation of the fifth carpometacarpal joint and comminution of the dorsal hamate rim. Finally, type III lesions exhibited coronal splitting of the hamate.

Histophysiology of a primary immune response against Aeromonas hydrophila in carp (Cyprinus carpio L.)

AbstractHistological and immunological parameters were monitored in carp during the primary immune response against Aeromonas hydrophila. Localization of antigen in the spleen initially ocurred in the ellipsoids, whereas in the head and trunk kidney it was diffusely distributed. When antibody titers increased (from day 9 onwards), antigen accumulated in melano‐macrophage clusters in all three organs, and it was mainly bound to cell membranes. Tissue‐bound immunoglobulin was present on several structures in the lymphoid organs. As a consequence of immunization, the number of cells with cytoplasmic immunoglobulin and the amount of immunoglobulin associated with the reticular sheath of ellipsoids and membranes of melano‐macrophages increased. Pyroninophilia was limited, and occurred in the spleen associated with ellipsoids; in addition, clusters of cells appeared, displaying a small rim of pyroninophilic cytoplasm. In the kidney the reaction was not conspicuous. The number of antibody forming cells in the head kidney peaked at day 9 and the serum antibody response followed with a peak at day 15. When the antigen was emulsified in adjuvant, the antigen processing and the antibody responses were affected. Antigen processing was retarded and a second burst of antibody production occurred from day 15 onwards. The relationship of melano‐macrophage centers with immunological processes is considered. It is suggested that in fish these centers might be primitive analogues of the mammalian germinal centers.

The involvement of dendritic cells in the handling of the immune stimulant C. parvum. A morphological investigation using immunoperoxidase techniques.

In earlier experiments we showed that locally administered Corynebacterium parvum (C. parvum) stimulated the T-cell system and had a beneficial effect on the recurrence rate of surgically resected cancers of the uterine cervix. In this paper we report the use of an immunoperoxidase technique to trace C. parvum antigen in the draining lymph nodes. In a guinea pig model the popliteal lymph node was studied after the injection of 70 micrograms of C. parvum in the hind footpad. At 6 h, intact bacteria were detected in sinus histiocytes. A transient granuloma formation was apparent between days 2 and 6, originating in the subcapsular and interfollicular areas. Three antigen-positive cell types were observed in these granulomas: a) cytophagocytic macrophages which were weakly positive, the antigen being distributed in clumps; b) dendritic cells with a strong, fine-granular positivity and c) some epithelioid cells with a small positive cytoplasmic rim. The majority of epithelioid cells was negative. Antigen-positive dendritic cells were also observed just beyond the granulomas in the T-dependent paracortical area. These cells are known as interdigitating cells (IDC) and present antigen to T-cells. Ten days following C. parvum injection the lymph node follicles became positive and the antigen could be detected in the long cellular protrusions of the dendritic reticulum cells (DRC). DRC probably play a part in immunological memory by trapping antigen in the form of immune complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

The morphology of the amelanotic Greene melanoma.

Pieces of amelanotic Greene melanoma were transplanted onto the iris surface of rabbit eyes, where they started to grow rapidly after a dormant period of four to five days. Light microscopically, the melanoma cells appeared round or polygonal and contained large, lightly staining nuclei and prominent nucleoli. Electron microscopy revealed rather electron translucent nuclei containing only a small rim of heterochromatin immediately subjacent to the nuclear envelope. The very prominent, reticulated nucleoli frequently lay close to the nuclear surface. The cytoplasm of the cells showed a well developed Golgi field which contained myriad vesicles of different shape and density and cross-striated, membrane-bound organelles of early melanin synthesis. The mitochondria were short and the smooth-surfaced endoplasmic reticulum was inconspicuous. The rough-surface endoplasmic reticulum was sparse and exhibited predominantly short segments. Like other very active cells, the melanoma cells contained a multitude of ribosomes. Melanoma cells which were not completely surrounded by other cells exhibited numerous processes at the free cell surface and, directly subjacent to these, a layer of very electron dense cytoplasm, indicating that these cells may possess a certain amount of motility. Many light and electron microscopical aspects of the amelanotic Greene melanoma are identical or similar to human uveal melanomas, especially of the epithelioid variety. On morphological grounds it is therefore possible to suspect a close biological relationship of these tumors. Thus, the use of the Greene amelanotic melanoma as a model for study of diagnostic and therapeutic problems in ophthalmology may be considered adequate.

The Fine Structure of Uterine Sarcomas

This paper describes the ultrastructure of uterine sarcomas, which are considered under two major categories — endometrial sarcomas and leiomyosarcomas. Endometrial sarcomas show a wide range of cytological and histologic patterns. On the basis of morphology it seems appropriate to distinguish between three subgroups: - pure homologous endometrial sarcomas - pure heterologous endometrial sarcomas - mixed mesodermal tumors (MMT) with or withour heterologous elements The mixed mesodermal tumors (MMT) contain different types of sarcoma and carcinoma mixed together. The carcinomatous components may be adenocarcinoma of endometrial or tubal type, undifferentiated carcinaoma, squamous or clear cell carcinoma. The differentiation of these elements is organ- or system-specific in the sense that it reflects the epithelial potentialities of the Müllerian duct. To a certain degree the sarcomatous elements of MMT represent more or less distorted reflections of normal - hormone dependent - tissue reactions of the endometrial stroma. Thus on the basis of our morphologic findings we distinguish 4 homologous cell types: 1) undifferentiated tumor cell (tumor stem cell) 2) “fibroblastic” tumor cell 3) neoplastic granular cell 4) leiomyoblastic tumor cell Most authors agree that the undifferentiated tumor cells in MMT are derived from the endometrial stromal cell. Thus this neoplastic cell and its normal counterpart are characterized by a large nucleus and a small rim of cytoplasm with only few organelles. The “fibroblastic” cell closely resembles cells of the mid-secretory cycle. Cytoplasmic organelles and specializations of the cell surface indicate a synthesis of collagen. A second homologous cell differentiation is the neoplastic granular cell, which on the basis of histochemical and electron microscopic findings is a complete reflection of the normal granular cells of the endometrium. The latter are most specific to the functioning endometrium, and accordingly are found in large numbers in the late secretory phase of the endometrial cycle. Another homologous cell element is the leiomyoblast which, when fully differentiated, contains tracts of longitudinally oriented myofibrils. The best known heterologous elements in MMT are rhabdomyosarcoma, chondrosarcoma, and far less often osteo- and liposarcoma. It is now generally assumed that differentiation to these tissues represents neoplastic mesenchymal metaplasia of the tumor cells of MMT. Thus the ultrastructural findings show the development of highly differentiated rhabdomyoblasts or neoplastic cartilage from immature sarcoma cells. From our findings it can be stated that the neoplastic stromal cell has a many fold mesenchymal potency, which is especially realized in MMT. Contrary to the mesenchymal elements, the epithelial components strictly retain their Müllerian character. Pure heterologous sarcomas are probably very rare. They are characterized by just one line of differentiation. Pure homologous sarcomas are not yet fully defined, although we presume that on account of its cellular features it may be regarded a “stem cell sarcoma” of the endometrium with occasional differentiation into “fibroblastic”, smooth muscle tissue, neoplastic granular cells, or decidual cells. Electron microscopic studies on leiomyosarcomas disclose a wide range of cytologic differentiation. According to cytoplasmic appearance three main cells can be distinguished: un(de)differentiated cells, myoblastic cells, and fibroblast-like cells. Derivation of these cells from the smooth muscle cell of the uterine wall is suggested. The cytoplasm of more differentiated tumor cells usually contains focal myofilament bundles. The low cytoplasmic organization of undifferentiated cells is considered a sign of dedifferentiation, while the fibroblastic tumor cell may show the dual potentiality of smooth muscle cells.

Prostaglandin induced shape changes in fibroblasts grown in cell culture

PGE 2 induced shape changes in porcine adventitial fibroblasts grown on glass in low density monolayer cell cultures. Incubation of the cells with PGE 2 at concentrations of 100 ng/ml and 1000 ng/ml induced rounding of flat fibroblasts within one hour. The rounded cells had a small rim of cytoplasm around the nucleus and from one to several long thin arborizing cytoplasmic processes extending outward along the substratum. Removal of the PGE 2 resulted in transient blebbing of the cell membrane of both the cell body and the processes as the cells returned to their flat normal morphology within one hour. The effect could be inhibited by 1% fetal calf serum. PGF 2α did not however induce similar changes. This difference between PGE 2 and PGF 2α is similar to a report on spreading and migration of mouse peritoneal macrophages, and suggests that under certain conditions PGE 2 may have the ability to induce shape changes in cells.

The zero pivot phenomenon in transportation and assignment problems and its computational implications

Transportation and assignment models have been widely used in many applications. Their use was motivated, among other reasons, by the existence of efficient solution methods and their occurrence as sub-problems in the solution of combinatorial problems. A previous study [10] observed that, in large-scale Transportation and Assignment Problems, 95 percent of the pivots were zero or degenerate pivots. This study investigates the ratio of zero pivots to the total number of pivots and verifies the above observation under conditions of small rim variability. Rules are introduced that pay special attention to the zero pivot phenomenon, and significantly reduce CPU time in both phase-1 (generating the initial basic feasible solution) and in phase-2 (selecting the variable leaving the base and the variable entering the base). When these rules were applied, they reduced the CPU time substantially: a 500×500 assignment problem was solved in 1.3 seconds.

Effects of parenteral nutrition with lipids on the human liver. An electron-microscopic study.

The ultrastructural findings in the Kupffer cells of a liver biopsy of a 5-week-old baby, who had received repeated i.v. administration of Intralipid (10%) in a dose of 20 ml/kg body weight/day for 12 days, are presented. Heterophagocytosis of free lipid droplets occurs by invagination of the Kupffer cell membrane. Large, solitary or conglomerated fat droplets surrounded by a membrane (lipophagosomes) are present within the hypertrophic and most active Kupffer cells. Small, round or elongated dark bodies (primary lysosomes) are linked with and/or seem to fuse with these lipophagosomes. In addition, smaller phagosomes almost completely surrounded by a dark small rim and a less electron-dense center probably represent (further stages of the lysosomal breakdown. The latter is also expressed by the condensation from the periphery towards the center of the original lipid droplets enclosed within the lysosomes. Angular inclusion bodies, build up of lipid remnants and a granular matrix of medium electron density, constitute far advanced stages of lysosomal digestion and represent the development or transformation of the phagocytosed lipids into lipogenous pigments. On the electron-microscopic level a distinction between lipofuscin granules and ceroid pigment can hardly be made at that stage. These pigment granules can be found in various amounts within the Kupffer cells and can stay there for a long time. This accumulation probably inhibits the clearance capacity of the cellular elements of the hepatic reticuloendothelial system. The hepatocytes and spaces of Disse seem not to be directly involved in the process of fat phagocytosis and breakdown as summarized above.

Presynaptic dendrite cells and two other classes of neurons in the superficial layers of the superior colliculus of the chimpanzee.

In the superior colliculus of chimpanzee, three classes of neurons can be identified by ultrastructural criteria. They are 1) marginal cells located in the stratum zonale, 2) collicular relay cells in the stratum griseum superficiale and 3) presynaptic dendrite (PSD) cells, i.e., neurons with presynaptic specializations in soma and/or dendrites. PSD cells are the smallest neurons in the stratum griseum superficiale; they have a relatively large, deeply infolded nucleus and a small rim of cytoplasm rich in free ribosomes. PSD cells are sufficiently different from the two other classes of neurons to be reliably identified at the ultrastructural level. They closely resemble presynaptic neurons as described in the lateral geniculate nucleus of other mammalian species. Presynaptic dendrites in continuity with PSD cells are rich in organelles, especially ribosomal cluster, and establish en passage contact with other dendrites. Another type of presynaptic dendrite, poor in organelles, except for bundles of microtubules, could not be traced back to its parent neuron. Homo- or heterogeneity of PSD cells is discussed. No amxon was traced from a PSD cell.

Identification and characterization of the monoblast in mononuclear phagocyte colonies grown in vitro.

A liquid culture technique for growing mononuclear phagocyte colonies on a glass surface is described. This useful and reliable technique made it possible to study immature mononuclear phagocytes. In the mononuclear phagocyte colonies the cells grow separate from each other in a single layer. Three types of cells are recognized in these colonies, namely nondividing macrophages, and proliferating promonocytes and monoblasts. The macrophage and the promonocyte exhibit the typical characteristics previously demonstrated by the other methods, whereas the monoblast could only be fully characterized by the present liquid culture method. This proliferating cell (labeling index with [3H]thymidine, 92-96%) is almost round (diameters, 10 X 10 mum), has only a small rim of strongly basophilic cytoplasm, almost devoid of granules, and shows a certain degree of ruffling of the cell surface. The monoblast is positive for esterase with alpha-naphthyl butyrate as substrate (91%), for peroxidase (78% in the peroxidase-positive colonies), and lysozyme (43%). The monoblast is able to pinocytize dextran sulphate (15-20%) and to phagocytize opsonized bacteria (20-30%), latex particles (47%), and IgG-coated red cells (96%). IgG receptors (94%) and complement receptors (16%) are present at the cell surface. In these respects the monoblast has the typical characteristics of the mononuclear phagocytes, but its properties show it to be a more immature cell type than the promonocyte. On the basis of these criteria and the sequence of appearance of the different cell types during incubation and during the development of the individual mononuclear phagocyte colony, monoblasts being present before promonocytes appear in the colony, it is concluded that the monoblast is the precursor of the promonocyte. In these cultures granulocyte colonies are also formed, consisting of myeloblasts, (pro)myelocytes, stabs, and polymorphonuclear neutrophils. Besides the typically tight structure of this kind of colony, the granulocytic cells themselves are quite distinct from the mononuclear phagocytes by their morphology, cytochemical characteristics (e.g. all negative for esterase with alpha-naphthyl butyrate, but 96% positive with N-acetyl DL-alanyl 1-naphthylester), functional characteristics (pinocytic index 13-21%; phagocytic index; for opsonized bacteria 15-36%, for latex particles 10%, and for IgG-coated red cells 0%), and their very small number of IgG receptors and lack of complement receptors. On the basis of these criteria, these granulocytic cells are easily distinguished from the immature cells of the mononuclear phagocyte colonies. The present study confirms the conclusion that the mononuclear phagocytes are a separate cell line, quite distinct from the granulocytic series, since even the most immature cells so far identified--the monoblast and the myeloblast--have quite different characteristics.