A factor was found in Vibrio parahaemolyticus which inactivated the hemolytic activity of a purified, thermostable direct hemolysin. The inactivating factor was associated with the hemolysin but could be separated from it by diethylaminoethyl-cellulose column chromatography. The inactivating factor was activated by heating at 50 to 60 C, but was itself thermolabile and lost activity on heating to 70 to 100 C. The mechanism of the Arrhenius effect, observed with crude hemolysin of V. parahaemolyticus, is as follows. At 50 to 60 C, the temperature-dependent inactivating factor associated with hemolysin inactivates the hemolysin, whereas at 80 to 100 C the crude hemolysin retains activity because at this temperature the factor is inactivated.

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Single unit activities were recorded from the preoptic and anterior hypothalamic (POAH) explants obtained from newborn mice brain to study neural temperature sensitivities in the period of 10-34 days culture. The firing rate of recorded units was less than 13 impulses per sec at 35°C. Fifteen warm sensitive, 2 cold sensitive and 37 thermally insensitive units were obtained. The temperature sensitivities of the cultured POAH neurons were similar to those of in vivo neurons, i.e. the discharge frequencies changed smoothly in proportion to 1-5°C changes in local temperature.The thermal responses of warm sensitive units increased after 18 days and decreased over 30 days in vitro. Two warm sensitive neurons were identified and observed under the optical microscope. The cold sensitive units were unable to be recorded until about 20 days in vitro. It became evident that the neural temperature sensitivities of POAH neurons were maintained in an absence of the extrahypothalamic afferents, temperature-sensitive neurons; hypothalamus; organ culture; temperature regulation

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