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It has long been known that, in contrast to the range of variation of body dimensions, the semicircular canals of different animals are approximately similar in size. In the present study, measurements of the internal radius ( r ) and radius of curvature ( R ) of the endolymphatic canal were made in 87 species, comprising 46 mammals, 17 birds, 17 fishes and 7 reptiles, using specimens, and photographic records of specimens, already available. Using the principles of dynamical similarity, theoretical arguments are adduced which predict that if Steinhausen’s (1933) interpretation of semicircular canal function is correct there should be very slow increases, systematic but discreet, of r and R with body mass ( m ). The results of the measurements largely confirmed the theoretical prediction, the actual relations obtained for all species together being: log 10 100 r 2 = 0·0945 (±0·0549) log 10 m +0·2519 and log 10 100 R = 0·0761 (±0·0402) log 10 m + 2·3797 (where r and R are measured in mm and m in kg), similar relations being obtained for each class examined. It is shown that the observed changes in r and R can to a large extent account respectively for the changes in canal sensitivity and the time constant of cupular return which the theory suggests should be called for by changes in animal shape and body mass.

A NEED having arisen in this Institute for the measurement of the thermal conductivity of blood, the opportunity was taken to enlarge the scope of the investigation to include a number of biological fluids. Values near body temperature have been obtained for rat blood, human blood, centrifuged human blood corpuscles, human blood plasma, cow's milk, skimmed milk, top of milk, cream, egg white, egg yolk, and cod liver oil, and a correlation has been found between thermal conductivity and water content for these and other body materials for which data are available.Most of the fluids investigated deteriorate quite rapidly, and some are not easily available in samples of more than a few ml. Therefore an apparatus was required which would allow reasonably quick measurements to be made on small samples over a limited range of temperature with an accuracy to within a few per cent. A survey of the literature shows that these apparently simple requirements are not easy to satisfy. Such a survey has been made recently by Challoner and Powell (1956), who have also made new measurements on seven liquids. The fact that during the past thirty years or so, values ranging from 0.00127 to 0.00165 cal cm-l s-l Oc-l have been published for the thermal conductivity of water a t 5 0 " ~ is sufficient indication of the difficulties encountered in this type of measurement. Nevertheless, the values obtained recently by Riedel (1951), and by Challoner and Powell themselves, for some of the common liquids are almost certainly accurate to within about 1%. These best values were obtained by absolute methods demanding high precision in the measurement of such quantities as the electrical energy supplied to the heating element and the dimensions of the liquid space. Also rather elaborate procedure, including careful control of temperature, is required and is time-consuming. For routine measurements the comparative method to be described was preferred, any systematic errors introduced being accepted in return for the considerable advantages of speed and simplicity of operation.

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