H. Meyer

Bio: H. Meyer is an academic researcher. The author has contributed to research in topics: Blepharoplast. The author has an hindex of 5, co-authored 5 publications receiving 125 citations.

Electron microscopic study of Trypanosoma cruzi in thin sections of infected tissue cultures and of blood-agar forms.

Abstract: Thin sections of Trypanosoma cruzi in tissue cultures and from blood agar medium have been examined with the electron microscope.In the leishmania and crithidia forms of the parasite a neat separation of kinetonucleus and blepharoplast has been obtained and these structures are described. The blepharoplast is the row of basal corpuscles which give origin to the axial fibres of the flagellum.Division of the parasite seems to begin in the basal corpuscles; it is followed by binary division of the kinetonucleus and only later by fission of nucleus and cytoplasm.During the development of the leishmania into the crithidia form, the kinetonucleus and basal bodies are dislocated towards the posterior half of the trypanosome. The migration of these two structures and the consequent lengthening of the flagellum causes the surface membrane of the flagellum to be pushed inwards to form a deep invagination, so that the flagellum comes to the surface of the body and is separated from it along its whole length by its own sheath.In the adult form of the parasite a great vacuole is formed near the posterior tip of the trypanosome. It has no definite structure in the electron microscope, is transparent and seems to be filled with a liquid content. The basal corpuscles are situated in this region near the wall of the vacuole. The typical structure of the kinetonucleus could not be identified with certainty in these forms; it seems to be altered by the formation of the vacuole.The vacuole is crossed by a fibre system which comes from the body of the trypanosome and is often dislodged by the size of the vacuole. This fibre system ends in a sharply pointed process of varying length.The cost of reproduction of figures was defrayed by the Instituto de Biofisica da Universidade do Brasil.

Electron Microscope Study of the Exoerythrocytic Form of Plasmodium gallinaceum in Thin Sections of Infected Tissue Cultures

Abstract: SYNOPSIS. The exoerythrocytic forms of Plasmodium gallinaceum in thin sections of infected tissue cultures have been examined with the electron microscope. It was seen that important changes occur in the fine structure of the parasite during the various phases of the cycle. The cytoplasm of the merozoites at the beginning and at the end of each cycle shows a great electron density due to a fine granulation. Larger granules are found at one pole of the parasite. The merozoites have a large nucleus in the center, and an oval body of great electron density at one pole, the significance of which is unknown. Short canaliculi can also be seen in the cytoplasm, but no mitochondria have been found. The cytoplasm of the schizonts shows a low electron density. It contains small particles scattered irregularly throughout its whole mass. The nuclei are not well defined; the oval body observed in the merozoites apparently has disappeared. Short canaliculi are present everywhere; however, mitochondria could not be identified with certainty. In the final phase of the cycle, in the rosette formations, the cytoplasm assumes again the fine granular structure. The future merozoites are grouped around a cytoplasmic core, with which they are directly connected. The whole segmenter is situated in a vacuole formation. In cross sections of the merozoites an opening in the central pole has been observed.

An Electron Microscopic Study of the Final and Initial Forms of Plasmodium gallinaceum in Thin Sections of Infected Tissue Cultures

Abstract: SYNOPSIS. Merozoites from Plasmodiunz gallinaceum (exoerythrocytic forms) have been observed with the electron microscope in thin sections of infected tissue cultures. When still in segmenter formation, at the end of the intracellular cycle, a small canaliculum can be observed in their proximal part which runs from the nuclear region down into the cytoplasmic core of the segmenter, where, in some sections, it continues directly into the endoplasmic reticulum of the core. Large, vacuole-like empty spaces in the merozoites recall swollen mitochondria. They show short villi at the periphery, instead of the typical cristae; they resemble the mitochondria of starved tissue cells. In the distal pole of the merozoites, one or two oval bodies of great electron density are present, among several smaller granules, both structures still being of unknown significance. The rest of the cytoplasm is of great electron density and shows a fine granulation. In the young trophozoites the oval bodies and the smaller granules disappear. Also, mitochondria are not found just after parasites enter a cell. These, however, reappear soon. The contact of the trophozoites with the cytoplasm of the host is intimate. Both surface membranes of the parasite are visible, mostly intact, but showing also openings which are considered artifacts, since no images have been obtained which indicate a passage of material through them from the host to the parasite. It is believed, however, that the parasite takes up material from the host through the membranes by an osmotic process. The fading of the electron density and the greater distance between the particles of its cytoplasm in the growing parasite seem to prove this. The particles which are responsible for the electron density of the merozoites, and of the young trophozoites, do not differ in their aspect from the RNA particles of the host cells. The nucleus, which in the merozoites and in the very first intracellular stages shows a homogenous fine and dense granulation, develops a darker region later, of irregular shape, which is located eccentrically, and is considered the nucleolus of these forms.

Electron Microscopic Observations of Toxoplasma ' Nicolle et Manceaux ' grown in Tissue Cultures. (First Note.).

Abstract: Toxoplasma ‘Nicolle et Manceaux’ has been examined in the electron microscope in in toto preparations from tissue cultures. The extracellular as well as the intracellular forms of the parasite are too thick for an adequate penetration of the electron beam, and the inner structure of Toxoplasma is not revealed in these preparations. The whole parasite is covered by a very delicate, transparent mantle which may extend to form large membranes. They show no structure in the electron microscope. No sheath has been observed which protects the shape of the parasite. Most of the free forms have an irregular surface and tend to become flat and large. Several pictures illustrate the way in which Toxoplasma penetrates the tissue cells. In the beginning of parasitism the limits between cytoplasm and parasite are difficult to recognize. The region of the cytoplasm around the parasite is gradually dissolved and a vacuole is formed.

Chagas' disease and Chagas' syndromes: the pathology of American trypanosomiasis.

Abstract: Publisher Summary Chagas' disease-like all really great and important discoveries-has its own and very peculiar history, called by Magalhaes , a “tragicomedy, which embittered and destroyed the life of one of our greatest compatriots”. In this history it is useful to distinguish the following six periods. Chagas in 1908 discovered in the intestine of the blood-sucking triatomas that were common in the primitive huts of the Brazilian hinterland, an unknown trypanosome, which was named by “Schizotrypanum cruzi.” The presence of this parasite in bugs suggested to him the possible existence of an infectious disease in animals and man. Soon afterwards Chagas also found the parasites in the blood of domestic animals (dogs and cats) and in the blood of a sick child with a high temperature. The discovery of American trypanosomiasis by Carlos Chagas represents one of the most fascinating events in the history of medicine. It is almost incredible that such severe pathological manifestations, which represent the “causa mortis” of one third of our autopsy material, would have been overlooked or unknown before Chagas' unique discovery. American trypanosomiasis shows a very peculiar pathology of homeostasis of the human organism, and represents even today a new realm in pathology, which becomes understandable through Cannon's law of denervation.

A revised classification of the phylum protozoa.

Abstract: SYNOPSIS. A classification of the phylum Protozoa at supra-familial levels is given with definitions or descriptions of all of the involved taxa, some 140 in number. The scheme represents the result of the cooperative efforts of an international group of specialists and consultants who have‘been studying the overall problem for the past several years. Innovations of a nomenclatural nature have been held to a minimum, aside from the use of a system of uniform endings, but several major shifts of taxonomic significance have been introduced at all levels treated, including the subphyla. These revisions are explained in appropriately placed footnotes.

Trypanosoma cruzi: mechanism of entry and intracellular fate in mammalian cells.

Abstract: The mode of entry and intracellular fate of epimastigotes and trypomastigotes of Trypanosoma cruzi in cultured cells was studied. Electron microscopic observations indicated the uptake by phagocytosis of both forms into mouse peritoneal macrophages and of trypomastigotes and transition forms into other cultured cell types. In each instance the organisms were initially surrounded by a plasma membrane-derived phagosome. Trypsin and chymotrypsin treatment of the macrophages completely abolished attachment and ingestion of both forms, indicating that protease-sensitive structures on the macrophage plasma membrane mediate ingestion. The macrophage Fc or C3b receptors were not essential for uptake of T. cruzi in the conditions used. Cytochalasin B inhibited ingestion but not the attachment of both forms by macrophages. Epimastigotes were not taken up by HeLa, L cells, and calf embryo fibroblasts. In macrophages, epimastigotes were killed and digested within phagolysosomes. In contrast, trypomastigotes and transition forms escaped from the phagocytic vacuole and then multiplied in the cytoplasmic matrix. Amastigotes released from infected cells exhibited properties similar to those of trypomastigotes and were able to enter all cell types studied and multiply intracellularly.

Cell Biology of Trypanosoma cruzi

Abstract: Publisher Summary Among the protozoa of the Trypanosomatidae family, a large number of species represent agents of diseases, such as Chagas' disease. This chapter reviews some aspects of the cell biology of Trypanosoma cruzi, giving emphasis to those aspects related to the ultrastructure of pathogenic protozoa. Protozoa of the Trypanosomatidae family show, during their, life cycle, several forms which can be easily identified by light microscopy in Giemsa-stained preparations. The chapter also explains the life cycle of T. cruzi. In the life cycle of T. cruzi, there are forms which are able to divide. There is one form, considered to be highly differentiated and responsible for the infectivity of these protozoa, which does not divide. It is highlighted that the trypomastigote form can transform into a rounded form which possesses a free flagellum. This form, which appears in the stomach, is able to transform into either short epimastigotes that start a process of multiplication in the intestinum or into long epimastigotes which move to the more posterior region of the digestive tract of the bug. Cell surface is also emphasized in the chapter.