PRODUCTION AND UTILIZATION OF MILK solution into a vein and measuring the temperature of blood a little further downstream. The extent to which the blood temperature is reduced is inversely proportional to blood flow rate 1.6.2 Isotope studies Injection of radioactively labelled substrates, e.g. glucose, into the blood stream permits assessment of the milk constituents into which that substrate is incorporated. It may also be possible to study the intermediates through which biosynthesis proceedspo 1.6.3 Perfusion of isolated gland In many species, the entire gland is located such that it may be readily excised intact and undamaged. An artificial blood supply may be connected to cannulated veins and arteries(Figure 1.6): if desired, the blood supply may be passed through an artificial kidney. The entire mammary gland may Teat cannula Venous sa Oxygenator Figure 1.6 Diagram of circuit for perfusion of an isolated mammary gland of a guinea-pig, G, mammary gland; A, artery: v, veins( from Mepham, 1987)PRODUCTION AND UTILIZATION OF MILK 9 solution into a vein and measuring the temperature of blood a little further downstream. The extent to which the blood temperature is reduced is inversely proportional to blood flow rate. 1.6.2 Isotope studies Injection of radioactively labelled substrates, e.g. glucose, into the blood￾stream permits assessment of the milk constituents into which that substrate is incorporated. It may also be possible to study the intermediates through which biosynthesis proceeds. 1.6.3 Perfusion of isolated gland In many species, the entire gland is located such that it may be readily excised intact and undamaged. An artificial blood supply may be connected to cannulated veins and arteries (Figure 1.6); if desired, the blood supply may be passed through an artificial kidney. The entire mammary gland may thermometer Figure 1.6 Diagram of circuit for perfusion of an isolated mammary gland of a guinea-pig., G, mammary gland; A, artery; V, veins (from Mepham, 1987)