The Effect of Non-Suckling and the Non-Removal of Milk upon Individual Mammary Glands in the Lactating Mouse *

Whether lactation is a total response to suckling or whether an individual mammary gland must be suckled and drained for full secretory activity to be induced and maintained in it constitutes a controversial question. In guinea-pigs and rabbits, cessation of lactation and parenchymal involution occur in non-suckled glands as well as in glands which are being suckled but from which the removal of milk is prevented by ligation of the major galactophores.5' 6, 7, 8 Other workers, to the contrary, find that the mammary glands of rats continue to lactate under similar experimental conditions.9' 10, 11 The present study was designed to ascertain the degree of lactation in unsuckled and obstructed glands as well as to determine the general reaction of the parenchyma to these two conditions. The mouse is a favorable species for such an experiment because of the consistent level of secretory activity which is present in all glands during lactation, provided they are being suckled and drained.3 12 Cole3 has observed that some of the mammary glands of the mouse often show involutional changes when a very small litter is suckling.