496 NUTRITIONAL REQUIREMENTS 



products of hydrolytic cleavage of simple food substances, as 

 a mixture of simple sugars, higher fatty acids, aminoacids 

 and salts, make any further brain-racking efforts in this line 

 superfluous. This is, however, not to say that such arti- 

 ficially constructed food is fully equivalent to natural food ; 

 this is certainly not true. There are still a great many im- 

 perfectly studied factors involved which are to be taken into 

 consideration. For example, although it has not been found 

 possible thus far to indefinitely maintain the lives of pigeons 

 upon a mixture of simple food substances, this is apparently 

 due, as shown by studies in the Munich Physiological Insti- 

 tute, 31 simply to the physical character of the nutrient ma- 

 terial, which occasions severe inflammatory processes in the 

 crop of the birds. Contrary to divergent findings, 32 F. Koh- 

 mann has shown that mice can be kept alive very well on a 

 nutrient mixture of protein material, fats, carbohydrates and 

 salts. 33 What complicating factors are likely to enter into 

 this type of experiments is evident in the already presented 

 experiments of Stepp, 34 who found that mice would invari- 

 ably die in the course of a few weeks on a diet, otherwise 

 entirely sufficient, from which the contained lipoids had been 

 removed by means of alcohol and ether. 



A valuable recent study by T. B. Osborne and L. B. Men- 

 del 35 has been submitted in reference to rats, showing that 

 white rats serve as very suitable subjects for such investi- 

 gations. The normal length of life of these animals is about 

 three years; studies extending over the period of a year 

 therefore include a very considerable part of their term of 



81 L. Jakob (O. Frank's Lab., Munich), Zeitschr. f. Biol., 48, 19, 1906. 



82 W. Falta and C. T. Noegerath (W. His's Clinic, Basel), Hofmeister's 

 Beitr., 7, 313, 1905; P. Knapp (Basel), Zeitschr. f. exper. Pathol., 5, 147, 1908. 



88 F. Rohmann (Breslau), Allgem. med. Centralztg., 1908, No. 9, cited in 

 Jahresber. f. Tierchem., 38, 659. 



84 W. Stepp (F. Hofmeister's Lab., Strassburg, and Medical Clinic, Giessen), 

 Biochem. Zeitschr., 22, 452, 1909, and Zeitschr. f. Biol., 57, 135, 1911. 



35 T. B. Osborne and L. B. Mendel, 1. c., and Science, n. s., 84, 722, 1911; 

 Jour, of Biol. Chem., 12, 473, 1912; Zeitschr. f. physiol. Chem., 80, 307, 1912. 



