We have studied the accuracy of blood volume measurements using carbon monoxide (CO)-labelled haemoglobin (COHb) injection and dilution (CO method) by comparing changes in red cell volume (RCV) measured using the CO method and 51Cr-labelled erythrocyte dilution (51Cr method) in a haemorrhage and infusion model in rabbits. RCV was measured repeatedly using the CO method at four different blood volume stages (stages I-IV). At stages I and IV, RCV was measured simultaneously using the 51Cr method. In comparing the sum of the circulating RCV and extracted RCV (SUM RCV) using the CO method, the values were almost equal and there were no significant differences between the values at the four stages. In comparing circulating RCV measured using the CO method and the 51Cr method, mean difference between the two methods was 0.80 (SD 0.76) ml kg-1 or 4.7 (4.6)%, and a positive correlation was observed (r = 0.91). We conclude that the CO method can be used to measure blood volume during perioperative periods in infants because it avoids use of a radioactive tracer, is simple and repeated measurements are possible.

Working with the suprarenal vein blood, Sugawara reported, some years ago, from our Laboratory of the existence of a certain dif ference between the values of epinephrine therein determinable by two kinds of method, that achieved by the cat paradoxical pupil reaction being inferior to that arrived at by the rabbit intestine segment me thod. The mean of the ratio in 34 observations was noted as 1:1.7.1) The suprarenal extracts made from several kinds of animals were also estimated by the biological methods above mentioned, and the colori metrical method of Folin, Cannon and Denis. Kodama's modifi cation found its application. The values yielded by the three methods did not coincide with each other, but there existed certain ratios be tween them.2)Simultaneously with the second work of Sugawara, several investigations attacking the same line of thought and extending in several directions were started. The present investigation involving a large number of the methods and a large number of different ani mals was one of them, and the other papers have been reported prior to this. The latter involve the following data which will be recapitu lated in their order of appearing in this Journal.According to Kojima and Saito, the bovine suprarenal medulla extracted by Folin gives to the method of Folin and others and the 1) T. Sugawara, Tohoku J.

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Keywords Back-extraction rate, bis(dithizonato)zinc(II) 289 Letters to the EditorThe forward extraction mechanism of a metal ion with 3-mercapto-l,5-diphenylformazan (dithizone) has been extensively studied. In most cases the formation of the first ligand complex was rate-determining. ' However, little information on the process of back-extraction of a metal chelate has been obtained. In the present work, a method for the investigation of back-extraction mechanism is proposed. The rate-determining step of backextraction of bis(dithizonato)zinc(II) (ZnR2) was found to be the dissociation of ZnR2 in the aqueous phase.At first, it was assumed that the rate of back-extraction is first order with respect to the concentration of ZnR2 in the organic phase:where the subscript org, t and kobsd denote the organic phase, shaking time and the rate constant for backextraction of ZnR2, respectively. Eq. (1) giveswhere the initial concentration need not equal the concentration of ZnR2 added before shaking. If the above assumptions are valid, a plot of -ln[ZnR2]org,t against t should give a straight line having a slope of kobsd and an intercept of -ln[ZnR2]org,t=o. Then, the experimental procedure was as follows. Twenty cubic centimeters of an aqueous solution containing 0.1 mol dm 3 NaC104, whose pH was preliminarily adjusted by adding hydrochloric acid, were taken in a separatory funnel. An equal volume of chloroform solution containing 1.0X10.4 mol dm 3 ZnR2 was added, and the mixture was shaken vigorously at a definite time. After the phases were allowed to separate, the concentration of zinc(II) in the aqueous phase was measured with an atomic absorption spectrometer. The pH was also measured by using a glass electrode. All experiments were carried out at room temperature (ca. 298 K).Experimental results are given in Fig. 1; the plots fall on a straight line, showing that Eq. (2) is valid. The Plot of -ln[ZnR2]org ,t against shaking time (t) ; b, 2. 03; c, 2.83; d, 3.05; e, 3.21; f, 3.89; g, 3.93 pH: a, h, 4.26. Fig. 2 Plot of log kobsd against pH.

Since it was found by van't Hoff-Cohen1) that within certain limits of temperature van't H o ff's law of chemical reaction (Kanitz's RGT -l aw) is applicable to plant respiration also, numerous experiments have been made to find some definite relationship between temperature and bio logical processes and to examine whether it could be identified with any chemical law .2) There is no doubt that temperature has great influence on biological processes; the question at present seems to be whether the temperature effect can be expressed by a curve with exponential characters,2) by a straight line,3) or by some any other curve.Tissues cultivated in vitro are a very good subject to work with on this point, because of the ease of control of the conditions and the relative simplicity of measurement of growth.Not only is it important to investigate the temperature effect on the growth of tissue in vitro with a view to a physico-chemical explanation of growth but also from a practical and techinical point of view.