A revolutionary philosopher of science.
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History, 20th Century↗
Biomedical subjects
D L Hull
Publications and source records attributed to D L Hull.
Fluoride ingestion during multiple pregnancies and lactations: microscopic observations on bone of the rat.
Female rats were given 150 ppm fluoride in the drinking water during three successive pregnancy and lactation periods; the femoral diaphyses were then examined for morphological alterations by light and scanning electron microscopy to determine the influence of fluoride ingestion during multiple pregnancies and lactations. The periosteal surface was dominated by areas of woven bone formation with some prolonged resting areas around osteocyte lacunae. The endosteal surface consisted mainly of areas of active bone resorption with some areas of bone formation. The interior of the cortex was characterized by numerous resorption cavities and remodeling in secondary Haversian systems. Fluoride, by the nature of its incorporation into bone crystals and by its direct cytotoxic effect on bone resorbing cells, reduces the availability of calcium from bone. It appears that fluoride ingestion during lactation created a heightened state of calcium homeostatic stress. As a result, bone mineral was mobilized by resorption of the endosteal surface and by cavitation of the interior of the cortex. Secondary hyperparathyroidism is thought to play an integral part in an attempt to maintain calcium homeostasis.
Animals↗
Reduction and genetics.
Examples of reduction outside of physics typically concern in principle possibilities; e.g., if we had a decent psychological theory of human behavior, we could reduce it to neurophysiology once we know more. However, in one instance, a reduction is actually well underway - the reduction of Mendelian genetics to molecular biology. Empirical and conceptual difficulties in setting out this reduction have led certain philosophers to modify the traditional logical empiricist analysis of theory reduction, first, to allow for necessary corrections and, second, to introduce a temporal dimension [reduction, genetics, theory, logical empiricism].
Genetics↗
Cell proliferation of colonic neoplasms in dimethylhydrazine-treated rats.
We have measured mitotic indices and 3H-thymidine-labelling indices for the colonic epithelial tumours induced in rats by the administration of dimethyl-hydrazine (DMH). The fraction-of-labelled-mitoses (FLM) technique has been used to estimate the duration of the cell-cycle phases. In general, mitotic and labelling indices in the tumours are similar to those in the proliferation zone of the normal crypt epithelium; lesions considered to be least well differentiated on histological grounds appear to have the lowest mean labelling index. Benign tumours and the different types of malignant tumours have mean cell-cycle times about half those of the normal mucosa.
Animals↗
Cytokinetic changes in the thymus of tumour-bearing and of dexamethasone-treated mice.
Changes in the cell population kinetics of the Balb/c mouse thymus were studied (a) during the growth of a syngeneic transplantable sarcoma and (b) following intraperitoneal injection of dexamethasone. The weight of the thymus fell briefly after tumour transplantation, then recovered with overshoot and eventually declined profoundly. After dexamethasone injection the weight of the thymus fell to roughly one-third of its normal value in 36 hr. Similar cytokinetic changes were observed in both sets of experiments; thymic wasting was accompanied by a small increase in thymocyte cell cycle time, a prolongation of the S-phase of the cycle, a marked decrease in the thymocyte cell production rate and a marked reduction in the growth fraction of the thymocyte population in the superficial cortex. It is suggested that thymic atrophy in tumour bearing animals may be a stress phenomenon.
Animals↗