Quelques Donnees Ecologiques sur les Cilies Libres de l'Afrique

Several problems concerning the ecology of free-living ciliateProtozoa from the continent of Africa require and are worthyof in-depth study. But work already carried out, primarily bythe author alone, indicates several general conclusions of interest.The infusorian fauna of inter-tropical Africa, surprisinglyenough, is poor and little diversified, apparently due to unfavorableecological (mostly chemical-physical) conditions. Endemic species,however, are quite frequently found: of 130 species studied,23% were new. Finally, although the density of ciliates is oftenlow, in some cases populations of certain species have presenteda biomass which must play a role of definite significance inthe food-chain cycle in the habitats in which they occur.     

Studies of Blastocystis hominis

Blastocystis hominis, grown in Boeck-Drbohlav culture medium, modified by the omission of rice starch and the addition of 20% human serum and mineral oil cover to the Locke's solution overlay, can assume 3 morphologic forms. In the absence of human serum the vacuolated form, which divides by binary fission predominates. In medium with high serum content the granular form appears, with 3 types of granules. Spheroid or more elongate cytoplasmic granules predominate. In older organisms, lipid granules are found either in the peripheral cytoplasm or in the central vacuolar space. In occasional cells, variable numbers of reproductive granules develop in the central vacuolar space. These latter granules are released from the organism and give rise to typical B. hominis cells. The 3rd form, the ameba form, appears in small numbers in older cultures and in those treated with antibiotics. Ameba forms feed on bacteria and have slow pseudopodial activity. Exposure to oxygen causes rapid damage to cell membrane, with resulting leakage and collapse.     

Facts and Hypotheses Concerning the Control of Odontoblast Differentiation

Numerous studies using amphibians have demonstrated that preodontoblasts emerging from the dental papilla are derived from cranial neural crest cells [4, 12, 46, 64]. However this has not been established for mammals. The history of odontogenesis begins during the early stages of cranial-facial development when the maxillary and mandibular processes develop. Continuous epithelio-mesenchymal interactions condition the histogenesis and morphogenesis of the teeth [24–26, 43, 44, 49, 51,58] as well as the terminal differentiation of odontoblasts and ameloblasts [23, 47, 52, 54, 59, 61, 67].
During recent years a considerable amount of experimental data relating to differentiation of odontoblasts has been published. We summarize these data and attempt to integrate them in deductive hypotheses concerning the control of odontoblast differentiation.