“4. On account of the probability of its containing, when made under certain patents, unhealthy ingredients.” The two last grounds for condemning oleomargarine are evidently affected by, and, in fact, dependent upon the character of the fat and the exercise of care employed in its manufacture. In regard to the relative digestibility of butter and its imitations, actual experiments have been made by several chemists. A. Mayer,[46] from the results of feeding human beings for three days on butter and on oleomargarine, found that 1·6 per cent. less of the latter was absorbed by the system than of the former, and inclines to the opinion, that with healthy persons this proportion is so inconsiderable, that it is of little or no importance. Dr. Clark considers these experiments of too limited duration to be regarded as conclusive, although, so far as they went, the results reached coincided with those obtained by him by a more exhaustive investigation. Dr. Clark has made an examination of the artificial digestion of butter as compared with oleomargarine and other fats, including beef and mutton suet, and lard, cotton-seed, sesamé, and cod-liver oils. The method of examination pursued was as follows:--About 2 grammes of the melted fat was added to a digestive fluid consisting of 0·33 gramme of “extractum pancreatis,” and 0·33 gramme of sodium bicarbonate, dissolved in 10 c.c. of distilled water. This mixture was introduced into a test-tube, well shaken, and then exposed to a temperature of 40°. The contents of the test-tube were microscopically examined at the lapse of intervals of one, four, and twelve hours. It was found from these tests that cod-liver oil exhibited the most perfect state of emulsion, after which came genuine butter, next lard oil, and then commercial “oleo.” Plate VIII. represents the results obtained from the experiments made with butter and commercial oleomargarine, as presented at the end of one, four, and twelve hours. The globules of butter-fat, it will be observed, are smaller in size and more uniform in appearance. Dr. Clark likewise instituted experiments which tended to demonstrate the relative insolubility of the fats used in the preparation of artificial butter. PLATE VIII. [Illustration: Butter 1 hour × 250.] [Illustration: Oleomargarine 1 hour × 250.] [Illustration: Butter 4 hours × 250.] [Illustration: Oleomargarine 4 hours × 250.] [Illustration: Butter 12 hours × 250.] [Illustration: Oleomargarine 12 hours × 250.] ARTIFICIAL DIGESTION OF FATS. FOOTNOTES: [26] Journ. Amer. Chem. Soc., iii. p. 83. [27] The proportion of butyrine present in commercial oleomargarine is often sufficient in quantity to cause the characteristic odour of butyric ether to a noticeable degree. [28] Fresenius’ ‘Zeitschrift,’ 1879, p. 197. [29] ‘Zeitschrift für Analytische Chemie,’ 1877, p. 145. [30] The French standard is 87·50 per cent.