A survey has been made of the amount of muscle water available to inulin, sucrose, and radioiodinated human serum albumin (RISA). The percentage spaces available to the three molecules are of the same order of magnitude, but the sucrose space > inulin space > albumin space. The kinetics of influx and effiux of RISA have been studied, and it appears that a small part of the albumin may be adsorbed in the extracellular phase. Nevertheless the albumin space would appear to give the best index of the extracellular volume.The scatter in values found for the extracellular space by all methods is very great, ranging from 8 to 40 per cent and renders invalid the use of a mean value for the calculation of intracellular concentrations. The variation within paired muscles is less than between pairs, provided the tissue has undergone no volume change. Increase in total muscle volume when the muscle is placed in a hypotonic solution leads to a decrease in the size of the extracellular space.All work on the distribution of electrolytes between the external medium and the sartorius muscle depends for its interpretation on an estimate of the extraceUular volume of the muscle. This also applies to any attempt to relate the ionic gradients across the muscle membrane with the bioelectric potentials. It is consequently of prime importance to know the dimensions of the extracellular space, and the degree of variation in the dimensions of the space within a pair of muscles. Estimates of the extracellular volume of frog muscle in the literature range from 10 to 12 per cent (1, 2) to 35 per cent of muscle weight (3, 5, 7), depending apparently on the method of estimation, and the species of frog used.In this study we have attempted to clarify the situation in the following ways. First we have undertaken a comparison of the accuracy of the various methods of estimating the space. Second we have evaluated the scatter in values found in a population of animals, in order to ascertain whether it is legitimate to use a mean value when calculating intracellular concentrations.
At the end of 1946, one of us (F.H.S.) earried out a series of expei'iments in whieh were investigated various aspeets of Nembutal anaesthesia in rats at different body-temperatures. A year later these experiments were repeated (by K.H.S.) in full aud the results were statistically treated. Of the earlier series of tests, it is sufficient to say heie that tlie findings were fully supported and borne out in the later series, the results of which are here presented.In 1947, P'uhrnian published a paper covering part of the field of the present investigation, and used body-temporature as the measure of therm.il effects, rather than the environmental temperature as used by earlier workers. At high and low environmental temperatures, even without anaesthesia, small animals possess a fluctuating body-temperature; when they are anaesthetized, only the body temperature is a satisfactory thermal index.Here an attempt is made to point out the effects of body temperature and sex on tbe anaesthetic time and the mortality in rats injected with Nemhutal (sodium pentobarbital). THE EFFECT OF BODY TEMPERATURE.Brunton (1874) noticed that warmth prevented death in guinea-pigs given toxic doses of chloral hydrate, and suggested treatiug acute chloral poisoning with warmth. He used rectal temperatures in his work but most later workers, using barbiturates, did not. Raventos (1938), using Evipal in miee, found the duration of anaesthesia was 2-5 times as long at 20° C. as at 30° C, and shorter at 40° C. than at 30° C. Cameron (1939), giving pentobarbital to rats, found that the anaestbetic-time inereased as the environmental temperature decreased; he also fouud that warmth prevented death. Gaylord and Hodge (1J)44) showed a similar increase in anaesthctie-time with deerease of environmental temperature, when pentobarbital was injected subcutaneously into female rats.
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