In recent years the perfused mammary gland has been used by a number of workers in the study of milk secretion. The method is open to criticism because both the blood flow and metabolic rate may be much lower than normal (Linzell, 1954) and in the cow the incorporation of radioactive phosphorus very low (Barry, 1952). In contrast, the yields of milk obtained by Tindal (1957) Linzell (unpublished) in perfused goats' udders, which are technically easier to work with. We felt that a more detailed study of this preparation would indicate its reliability and limitations, and so help to assess the usefulness of mammary perfusion for biochemical studies.In the work to be described we have tried to decide whether milk can be secreted in isolated perfused glands, using three criteria:(a) the quantity and composition of the milk in relation to that produced by the glands in the conscious animal before perfusion; (b) the responses to variations in the availability of known milk precursors produced by alterations in perfusate flow and composition; and (c) the transfer of labelled substrates from blood to milk on the assumption that, given a steady blood concentration of a radioactive atom, a derived milk product should eventually have the same specific activity.Preliminary communications have been given to the Physiological

Recent work has emphasized that both glucose and acetate are important metabolites in the ruminant. Annison & Lindsay (1961) estimate that 33 % of expired C02 is derived directly from acetate in the fed sheep, and Annison & White (1961) find that, under these conditions, 23 % comes from glucose; both these values are sensitive to the nutritional state of the animal. Considerable quantities of both glucose and acetate are taken up by the goat udder in vivo [Linzell (1960); some of the values for glucose uptake in this paper were wrong and an erratum has been published in J. Physiol. (1962), 163, 1], but it is not easy to determine in the whole animal the relative amounts of C02 coming from each substance in the metabolism of the udder itself (Wood, Gillespie, Hansen, Wood & Hardenbrooke, 1959). It is technically easier in the isolated organ because (a) the addition of substrates can be controlled, (b) radioactive substances can readily be infused for long periods, so that steady-state levels are more likely to be reached, (c) the blood flow is known, and (d) the metabolism of only one organ is involved. Although glucose is not a significant precursor of milk fatty acids in the ruminant (Balmain, Folley & Glascock, 1954; Kleiber et al. 1955), considerable amounts of milk citrate come from glucose in the cow (Kleiber et al. 1955; Tombropoulos & Kleiber, 1961), and half the C02 from glucose may be produced by routes other than the pentose phosphate pathway (Black, Kleiber, Butterworth, Brubacher & Kaneko, 1957a). These discordant results suggest that the relationship between glucose, acetyl-CoA and the tricarboxylic acid cycle in the ruminant udder is not clear. Further work (D. C. Hardwick, J. L. Linzell & S. M. Price, unpublished work) to elucidate the metabolic routes of these substances by using inhibitors and substituents for glucose gave results that were difficult to interpret. In the presence of

DEMETHYLATION OF GRISEOFULVIN BY FUNGI 37 products resulting from the incubation of griseofulvin with Mucor ramannianub yielded no recognizable material, although an unidentified phenolic substance, m.p. 142-145°, was isolated from the culture filtrate. From the evidence available, this phenolic substance does not appear to be one of the metabolic products discussed here. SUMMARY 1. Incubation of griseofulvin with fungi gave rise to various demethylated metabolites. Thus, 7-chloro-4-hydroxy-6: 2'dimethoxy-6'-methylgris-2'-en-3:4'-dione (4-demethylgriseofulvin) was produced by Microsporum cani8, griseofulvic acid (2'-demethylgriseofulvin) by Botryt8 allii and 7-chloro-6-hydroxy-4:2'-dimethoxy-6'methylgris-2'en-3:4'-dione (6-demethylgriseofulvin) by Cercospora meloni8.

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