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.

SUMMARY. Cerebrospinal fluid and serum from 192 patients was analysed for the presence of intrathecally synthesized oligoclonal IgG bands using isoelectric focusing in an immobilized pH gradient pH 7-10. The sensitivity of this method for the diagnosis of multiple sclerosis (MS) was 95% (21 of 22), or 750/0 if patients with suspected MS were included. The specificity for the diagnosis of MS was 98%, or 96% if the suspected MS patients were included. The very high specificity may be because the intrathecally synthesized oligoclonal IgG associated with MS is more alkaline than IgG from serum and is better detected in an immobilized alkaline pH gradient.

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