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LITERATURE relating to the bovine blood-sugar level shows that there is no concord of opinion as to the normal value. Among the earlier workers the average values recorded range from 50 mg. per 100 cc. [Awdejewa et al., 1927] to 82 mg. per 100 cc. [Schwarz, 1928]. Hewitt [1930] reports values of 79-95 mg. per 100 cc. for dry cows and 50-63 mg. per 100 cc. for lactating cows, and quotes average values ranging from 41 to 80-120 mg. per 100 cc. from a number of other workers. Hodgson et al. [1932] give an average value of 53 mg. per 100 cc. for cattle over 2 years old, and Turk and Work [1933] give 51 mg. per 100 cc. as their average for lactating cows. While it is conceivable that part of this variability is due to the different methods of analysis employed, the question of the time of sampling must not be lost sight of as a possible factor.The question of diurnal variation has so far received little attention.Richter. [1928] [1932] sampled cows, which were fed at 6 a.m. and 4 p.m., at 7 and 10 a.m. and 1, 3 and 5 p.m., and obtained blood-sugar values of 51-4, 49-0, 50-7, 52-9 and 50-5 mg. per 100 cc. at these hours. Alleroft and Strand [1933] reported higher blood-sugar levels in the evening than in the morning with starving sheep.EXPERIMENTAL. In the course of regular sampling for blood considerable fluctuations of bloodsugar level in the dairy cows were observed, notably when a large number of cows were bled on the same day and the time of sampling was extended. The general tendency for the later-drawn samples to exhibit lower levels of bloodsugar suggested that there might be a steady diurnal decrease about this time, which might be part of a diurnal rhythm in the level of this constituent. The following work was therefore undertaken to test the question, the HagedornJensen blood-sugar technique being employed [1920].Exp. Table I.

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