A convenient method for obtaining bovine arterial blood

Abstract

Abstract The value, both academic and practical, of accurate knowledge regarding the mechanism of mammary secretion requires no emphasis. Our relative ignorance of what is actually going on in the mammary gland during its activity has been justly lamented from time to time by several writers. Attempts have recently been made to remedy this lack of knowledge, particularly in regard to the nature of the precursors, in the blood as it reaches the gland, of the characteristic milk constituents. It is with a major point in the technique of conducting experiments on bovine blood constituents that this paper is mainly concerned. An apparently direct method of obtaining information on the question of milk precursors is to make an accurate comparison between the composition of blood entering and that of blood leaving the udder of an actively lactating animal, the samples being taken approximately simultaneously. With due care, it is now possible to obtain useful information by this method. It does not, however, necessarily follow that a change in the amount of any given organic constituent of the blood during its passage through the mammary gland is due to such a substance being withdrawn to form a milk constituent. Part at least may be used up—in fact, some organic material borne by the blood must be used up—to provide the energy required for maintenance and secretory activity. The metabolic activity of the gland is evidenced by the marked change in the colour of the blood of the mammary vein as compared with the arterial blood, despite the speed (see following paper) with which blood flows through the gland.