Biochemical Studies of the Mammary Gland Function.

1. An experiment was carried out to determine quantitative changes in the lactose content.of the mammary gland of rats in pregnancy, at parturition, during lactation and at weaning.2. The lactose content was estimated by the semimicroquantitative method of Malpress and Morrison. Litters were allowed to suckle until just before the death of their mothers so that the milk retained in the mammary gland might be removed as completely as possible.3. Lactose was never found in the mammary gland during pregnancy, but appeared promptly at the ti me of parturition, namely, initiation of lactation, and the weaning was followed by a rapid decrease of lactose in the mammary gland. These findings were fairly well agreeable with the results reported by Kuretani, but were incompatible with the rasults given by Folley and Greenbaum who demonstrated the presence of lactose in the rat mammary tissue at tha beginning of pregnancy and there after. This difference seemed to be attributed to the different methods of lactose determination.4. Since no lactose was found in the mammary gland even at the late stage of pregnancy, a milklike substance was shown by histological examination to accumulate in ducts and alveoli at this stage, but it was, not the true milk. Therefore, the demonstration of lactose in the mammary gland seemed to be a criterion to determine the true lactation in the experiment of induction of lactation.