November 24, 1911] 



SCIENCE 



725 



Casein* Zeins 



Amino-acids Per Cent. Per Cent. 



GlycocoU 0.00 0.00 



Alanine 1.50* 9.79 



Valine 7.20* 1.88 



Leucine 9.35» 19.55 



Proline 6.70' 9.04 



Aspartie acid 1.39* 1.71 



Glutaminic acid 15.55* 26.17 



Phenylalanine 3.20» 6.55 



Tyrosine 4.50» 3.55 



Serine 0.50'° 1.02 



Oxyproline 0.23" • 



Histidine 2.50" 0.82 



Arginine 3.81" 1.55 



Lysine 5.95" 0.00 



Tryptophane 1.50= 0.00 



Diaminotrioxydodeeanio acid 0.75" 



Ammonia 1.61'^ 3.64 



Sulphur 0.76" 0.60 



Phosphorus 0.85" 0.00 



ments in whicli isolated and purified proteins 

 have been fed successfully." 



Without citing here the numerous failures 

 and the successive changes instituted in our 

 earlier trials, we may briefly call attention to 

 some of the purely " nutritive " factors which 

 have had to be taken into consideration. The 



' Osborne and Guest, Journal of Biological 

 Chemistry, 1911, IX., p. 338. 



" Osborne and Liddle, American, Journal of 

 Physiology, 1910, XXVL, p. 304. 



' Levene and Van Slyke, Journal of Biological 

 Chemistry, 1909, VL, p. 419. 



' Van Slyke, Berichte der deutschen chemischen 

 Gesellschaft, 1910, XLIV., p. 3170. 



* Abderhalden, Zeitsohrift fiir physiologische 

 Chemie, 1905, XLIV., p. 23. 



' Reach, Virchow's Archiv, 1899, CLVIII., p. 288. 



" Fischer, Zeitschrift fiir physiologische Chemie, 

 1903, XXXIX., p. 155. 



" Osborne, Leavenworth and Brautlecht, Amer- 

 ican Journal of Physiology, 1908, XXIII., p. 180. 



"Fischer and Abderhalden, Zeitschrift fiir 

 physiologische Chemie, 1904, XLII., p. 540. 



^ Osborne and Harris, Journal American Chem- 

 ical Society, 1903, XXV., p. 323. 



" Hammarsten, Zeitschrift fiir physiologische 

 Chemie, 1883, VII., p. 227. 



'° Of. Osborne and Mendel, Publication 156, 

 Part I., Carnegie Institution of Washington, 1911, 

 for the literature on these topics. 



energy requirement must obviously be satisfied 

 in an available form. A minimum protein 

 requirement must likewise be provided in any 

 event. Experiments which are to continue 

 over more than very few days must include a 

 suitable quota of inorganic salts — so-called 

 mineral nutrients. This is in itself a problem 

 of fundamental importance, the study of 

 which has barely been begun in any synthetic 

 way. One may, it is true, imitate the " ash " 

 of milk or blood; but the elements occur here 

 in combinations quite different from those 

 prevailing in the tissue fluids themselves or in 

 the native foods. The balance of acid and 

 basic groups, the changing need for individual 

 elements like phosphorus, calcium, chlorine 

 and iron, furnish a series of complex variables 

 which are probably as indispensable to certain 

 aspects of nutrition as they are unappreciated. 

 If to all this is added the uncertain signifi- 

 cance of the as yet largely unidentified com- 

 pounds such as cholesterol and phosphatides 

 which occur in all natural food mixtures, the 

 experimental difiiculties begin to appear in 

 their true light. 



Days 



Pig. 1. (Taken from Carnegie Publication No. 

 156, page 26.) Showing the continued decline of 

 a rat on a dogbiscuit-lard diet for 103 days. 



At the outset it is only fair to remark that 

 a successful feeding experiment with isolated 

 food mixtures is of greater import than a 



