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Two important activities of the rumen microorganisms are (1) lipolysis of the lipids containing esterified fatty acids that are ingested by the ruminant and (2) hydrogenation of unsaturated fatty acids (Garton, 1964). Comparisons of the fatty acid composition of the free fatty acids and the esterified lipids of rumen contents suggest that hydrogenation ofthe fatty acids does not occur until they are hydrolysed from glycerolipid (Garton, Lough & Vioque, 1961; Hawke & Robertson, 1964; Patton & Kesler, 1967). For example, Patton & Kesler (1967) found that the fatty acids of neutral lipids, polar lipids and free fatty acids isolated from the rumen contained 6-6, 7-1 and 70.0% of stearic acid respectively, whereas the same fractions

Rates of secretion of milk constituents (fat, protein, lactose, Na+ and K+) in the lactating goat were measured under normal circumstances and after injections of ouabain. In all experiments a close association was noted in the secretion rates for protein, lactose and K+. Under the influence of ouabain, the concentration of Na+ in the milk tended to rise and that of K+ to fall. The rate of milk fat secretion varied independently from the rates for the other constituents. It is reasonably assumed that the principal mechanism of milk protein secretion is by emptying of Golgi vesicles through the plasma membrane. The close correlation in rates for protein, lactose and K+ supports the contention that all three are assembled in Golgi vesicles and secreted by the same mechanism.

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