Although the experiments in this series can hardly be considered as ideal, being open to the criticisms raised in their discussion, yet the preponderance of evidence clearly shows that the ingestion of fat in the form of cream, or butter with potato chips, has a positive influence upon the metabolism. This is not in accordance with the results of Koraen,1 who found no increase in the metabolism after the ingestion of about 66 grams of fat. Aside from a few experiments in which a depression in the metabolism below the basal value was found in the latter part of the experimental period, we obtained no evidence supporting the general view of Gigon that the ingestion of fat results in a depression of the metabolism (see page 40). Gigon's most interesting and suggestive explanation of his experiments, namely, that the ingestion of a fat diet (olive oil) caused a depression of the digestive activity which is present even in the post-absorptive condition, finds no support in the results of our experiments. It should be borne in mind that Gigon used a pure fat, while all of our experiments were carried out with materials containing a certain proportion of other nutrients. It is difficult, however, to believe that the starch in the potato chips or the small amount of protein and lactose in the cream could have counterbalanced the effect observed by Gigon. We are inclined to consider that the depression in the metabolism reported by him was more apparent than real and that his findings are due to the faulty use of a basal value, determined a long time before the experiments were made. By the use of this value he assumed a constancy in basal metabolism which, while justifiable when severe muscular work is to be performed, is hardly permissible when small increments in the metabolism are to be expected, such as those following the ingestion of small amounts of food or even large amounts of fat.2

We may therefore conclude that the ingestion of fat produces a positive increment in the metabolism. Although the increment is considerably less than that observed with an equivalent amount of energy in either carbohydrate or protein, it is nevertheless a factor that must not be neglected in a consideration of the influence of the ingestion of food upon the metabolism. We are in full accord with Gigon in believing that a study of the effect on the metabolism of ingesting pure fat is highly desirable and regret that more experiments with olive oil or other pure fats were not included in our series.

1Koraen, Skand. Arch. f. Physiol., 1901, 11, p. 176. See, also, p. 32 of this publication.

2Personal acquaintance with Professor Gigon and a full appreciation of his high scientific conceptions of the importance of physiological research have led us to attempt to communicate with him personally regarding the adverse criticisms which we have felt it necessary to make in this report. While an acknowledgment of the receipt of the letter has been made, he states that it has been impossible for him as yet to take up in detail any of the criticisms which we raise, although he promises to send a letter to us shortly. Undoubtedly war conditions have made it impracticable for him to do this. It is a matter of great regret to us that we have been obliged to go to press without personal information regarding the criticisms here raised, so that if we are in error or have misinterpreted his attitude we might modify our expressions in such way as to fit the case more exactly.