Mat 31, 1918] 



SCIENCE 



537 



publication, and others, for one reason or an- 

 other, not satisfactory from which to draw 

 conclusions. Furthermore, it will be generally 

 cionceded that no one but the experimenter 

 himself has the right to the interpretation of 

 his data, for he must be responsible for the 

 correctness of such interpretation. 



I find on reexamination of the charts in 

 the paper by Miss Simmonds and myself in 

 the Journal of Biological Chemistry, 1917, 

 XXXIII., p. 303, that several of the curves of 

 growth were secured in experiments carried 

 out before our removal to Baltimore. I regret 

 that mention was not made of this fact. Most 

 of our papers contain data which was not se- 

 cured from a series of experiments carried 

 out simultaneously. The later experiments 

 are in most cases planned in the light of the 

 outcome of the earlier ones, the work being 

 continued until a complete demonstration of 

 some principle is secured. No injustice was 

 intended or will in future be done to the Uni- 

 versity of Wisconsin by witliholding proper 

 credit for the facilities which made the work 

 possible. The serial number of an experiment 

 signifies the period when a certain ration was 

 planned and entered in our notes and does not 

 throw any light on when the feeding trial was 

 made. 



In 1907 I began to build ui) my rat colony 

 at the University of "Wisconsin for the pur- 

 pose of studying the problem of the cause of 

 the failure of young animals to grow when 

 restricted to diets consisting of purified pro- 

 teins, starch, sugars, fats and suitable inor- 

 ganic salt mixtures. No one in this country 

 at that time had any interest in the enterprise 

 except myself, ify first publication describing 

 this work appeared in 1909, and antedated 

 that of any other of similar character by two 

 years. It required five years of fruitless ex- 

 perimenting before the first important ob- 

 servation was made which gave a clue to the 

 solution of the problem. In 1912, Miss Davis 

 and I first observed the peculiar growth-pro- 

 moting properties of butter fat. We had a 

 ration which we supposed consisted of food 

 substances essentially pure, with which we 

 could induce growth when butter fat was in- 



cluded to the extent of five per cent., whereas 

 the same food mixture containing such a fat 

 as olive oil or lard did not induce any growth. 

 For a time we believed that butter fat con- 

 tained the only chemically unidentified dietary 

 essential necessary for the promotion of 

 growth or the maintenance of health in a 

 mammal. By 1915, Miss Davis and I, after 

 making several hundred experimental feeding 

 trials variously modified, were forced to the 

 conclusion that a second unknown dietary es- 

 sential had been contained in the 20 per cent, 

 of supposedly purified milk sugar, which had 

 formed a constant constituent of many of our 

 early diets ; we thereupon propose a new work- 

 ing hypothesis concerning what constitutes an 

 adequate diet. This postulates the necessity 

 of two dietary essentials of imknown chemical 

 nature. 



After a long series of experiments planned 

 to show the distribution of these two sub- 

 stances in natural food-stuffs, it was found 

 that one of them is associated with certain 

 fats, whereas the other is never associated 

 with fats of either animal or vegetable origin. 

 The latter is soluble in water, the former 

 readily soluble in fats. Miss Kennedy and I, 

 therefore, proposed the terms fat-soluble A and 

 water-soluble B as provisional names pending 

 such a time as we should learn enough about 

 their nature to be able to give them names 

 which would be suited to their peculiar struc- 

 ture, and fit in with the nomenclature of or- 

 ganic chemistry. 



About two thousand feeding experiments 

 have now been completed, each lasting between 

 six weeks and two years. These were all in- 

 terpreted in the light of our working hypothe- 

 sis described above, and also in the light of the 

 composition of the proteins as revealed by the 

 studies of Fischer, Abderhalden, Osborne and 

 others, and have made clear the nature of the 

 dietary deficiencies of several representatives 

 of each of the several classes of natural foods, 

 seeds, tubers, roots, leaves, meats, eggs and 

 milk. These results have made possible impor- 

 tant generalizations, which must eventually 

 lead to great improvement in the health of 

 large groups of peoples who are now suffering 



