(With 9 flgores In the text.)The availability of "heavy" water D20 together with the accurate methods for its determination in weak solution in H20 have opened up new possibilities for the study of permeability problems.D,O and especially DHO which is predominantly present in weak solutions of heavy water behave in diffusion very nearly as normal water. The rate of diffusion of molecules in liquids depends namely in first approximation on the radius of the molecules alone. This was shown by Einstein to be the case for the movement of colloidal particles, and from the fact that numerous endeavours to separate radioactive isotopes through diffusion in liquids have failed entirely we conclude that Eins t eins considerations are also applicable to the diffusion of small molecules. The radius of D 2 0 is only 0.1 per cent larger than that of H20 molecules and the difference for DHO is still less, and we must assume that the diffusion coefficients of ordinary and heavy water will differ less than 0.1 per cent.The permeability of frogs skin has been studied before in a large number of experiments by Wertheimer, Pohle, Jurisic, Adolph and others. Without going into details we can state that on the basis of these experiments it is generally assumed that the skin allows water and certain dissolved substances to pass in, but resists in the living state the outward passage. It is claimed further (Adolph 1934) that in the living animal the nervous system influences definitely the rates of passage through the skin.

There is a debate whether supplemental feeding of deer bears the risk of inducing health problems, in particular acidosis. Here, the pH values of forestomach contents of free-ranging roe deer (Capreolus capreolus) shot in areas with and without supplemental winter feeding were compared. pH was similar in the dorsal and ventral rumen, but lower at these sites than in the Atrium ruminis, where it was again lower than in the reticulum; this pattern corresponds to expectations based on differences in the presence of saliva at the different sites of the forestomach. pH was lower with increasing time that elapsed between death of the animal and measuring pH in unsupplemented animals and was lower in unsupplemented animals in May/June than later in the year. Animals with supplemental winter feeding had significantly lower rumen pH (5.5) than animals without food supplementation (5.7). These data suggest that supplemental feeding of roe deer has the potential to lower forestomach pH. Although pH values measured in supplemented animals in this study would be considered indicative of rumen acidosis in domestic cattle, they are within the range previously measured in various free-ranging Odocoilid species, including roe deer; were of a similar magnitude as the May/June values of unsupplemented roe deer in this study; and must be considered with respect to potentially rapid declines in pH between death of the animal and pH measurement. Given methodological problems, analyses of literature data from free-ranging wild ruminants provide little evidence for a systematic variation of rumen pH with feeding type and body mass, but lead to the hypothesis that some New World cervids, including the roe deer, might either naturally have lower pH values than other ruminants or rumen contents whose pH drops rapidly after death.

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