The relationship in the cow between the osmotic pressure of milk and of blood

Abstract

SummarySimilar, marked variations in the freezing-point depressions of jugularvenous blood and of milk throughout a day were observed in cows when drinkingwater was offered for a single, short period each day. Values for milk were found to agree more closely, however, with those for mammary-venous blood than with those for jugular-venous blood. It appears that milk is in osmotic equilibrium with the blood flowing through the udder continuously throughout the period the milk remains within the udder and not only during its formation, and that milk secretion causes a slight alteration in the osmotic pressure of fluids within the immediate locality of the mammary gland. Changes in the milk composition that occurred in association with the observed changes in freezing-point depression were consistent with a movement of water into or out of the udder in response to any change in the osmotic pressure of blood.