By Margaret Lowenfeld

The fat content of both cow’s and human milk is a subject on which much work has been done, and though certain facts are now well established there is still no clear understanding of the circumstances which determine the normal range of variation or
knowledge of the conditions which determine these comparatively wide limits. In the course of our study on the composition of human milk in the early stages of lactation [Lowenfeld et al., 1927; 1928] it was noticed that the method of extraction of the milk sample had a considerable influence on the percentage of fat, although no other constituent was affected by this factor. Since this factor had not to our knowledge been investigated by any previous worker, it occurred to us that herein might lie the probable explanation of the variations in the fat percentage hitherto recorded. We decided therefore to undertake a more intensive study of the fat content in human milk throughout the whole course of lactation, paying special attention to the method adopted for obtaining the milk sample. The present paper is a record of our results and the conclusions which they suggest.