Abstracts of Communications

Abstract

in cow's milk but not in human milk. We have also examined the milk of goats, sheep, pigs and a mare. The milks of all the ruminants, cow, sheep and goat, contained xanthine oxidase. Milk from the sow and the mare resembled human milk in being devoid of the enzyme. To test whether these differences had a dietary basis the rabbit, which is herbivorous but non-ruminant, was examined and each of two does gave milk which contained xanthine oxidase. Oxytocin had to be used to obtain milk from the sow and rabbit. Analyses by an adaptation (Owen, 1957) of the dithiol method of Clark & Axley (1955) showed the presence of 30-60 pg molybdenum/l. in cow's milk. In human milk and pig's milk ashed with H,SO, + HC10, the molybdenum dithiol colour at 680 mp in the iso-amyl acetate extract was no greater than the blank for the reagents used. The failure to secrete xanthine oxidase may be a consequence either of a small intake of molybdenum or of an inability of the mammary epithelium of the non-secreting species to metabolize molybdenum.