The Non-utilization of Lactic Acid by the Lactating Mammary Gland.

Following the reports of Graham (3) and Shaw, Boyd, and Petersen (6) it has been generally accepted that the lactating mammary gland utilizes lactic acid. These reports were based on arteriovenous differences in which it was found that the mammary venous blood usually contained less lactic acid than the arterial blood. The arteriovenous lactic acid differences reported are extremely variable, especially for the goat. Graham’s data on goats show the relatively high average utilization of 16.7 mg. per cent with a range of 0.1 to 57.9. The arterial values appear unusually high, averaging 58.0 mg. per cent with a range of 10.0 to 134.3. The data of Shaw et al. on cows were also variable, showing a mean utilization of 3.64 mg. per cent with values ranging from a negative utilization of 1.55 to a positive utilization of 10.42 mg. per cent. The arterial values varied from 3.93 to 19.46 mg. per cent. It appeared advisable to attempt to obtain more nearly constant lactic acid differences which might be expected to be more representative of the normal metabolism of the gland. It was suspected that the large variations previously observed were due primarily to excitation of the animal during the drawing of the blood samples. Accordingly a reexamination was made of the r81e of blood lactic acid in milk secretion in which the usual method (Shaw and Petersen (7)) was used to determine whether the animal had been unduly disturbed during the drawing of the bloodsamples.