KOVBMBER 24, 1911] 



SCIENCE 



723 



the relative proportions of these constituent 

 complexes are so markedly different from the 

 average as to raise the question of compara- 

 tive nutrient values. Overabundance of glut- 

 aminic acid groups must necessarily be at- 

 tended by relative deficiency in other so-called 

 " building stones " of the protein fundament. 

 If, then, a minimum of some of these is an 

 indispensable requirement of tissue mainte- 

 nance or growth or repair, problems of relative 

 values at once suggest themselves.' To this 

 may be added the question of protein synthesis 

 in animals which has been so vigorously de- 

 bated in recent years. Here we touch upon 

 problems quite independent of the energy 

 needs of the organism, yet equally important. 

 No sooner has the idea of the isodynamic re- 

 placement of nutrients found acceptance, than 

 the practical limitations of this lav? are sub- 

 jected to critical examination. 



The foremost reason why so little is known 

 in the directions noted lies in the fact that the 

 individual foodstufTs have, with very few ex- 

 ceptions, rarely been examined heretofore in 

 respect to their actual nutrient role. Meat 

 and cereals have, it is true, been crudely an- 

 alyzed in terms of protein (NX 6.25), fat, 

 carbohydrate and ash, and fed as assumed 

 mixtures of the composition indicated. Physi- 

 ologists are, however, just beginning to recog- 

 nize the extreme chemical complexity of such 

 animal and plant tissues. How much of the 

 nutritive failures or successes shall be ascribed 

 to either presence or paucity of some inci- 

 dental component, as lime or iron, as lipoid or 

 nitrogenous " extractive " of specific physi- 

 ological import, such as is attributed to the 

 " hormones " ? 



It is, indeed, only in very recent years that 

 the perfection of biochemical technique has 

 permitted the preparation of isolated proteins 

 in what may be called comparative purity. 

 We believe, from the experience which one of 

 US has gained during many years of experi- 

 ment in this field, that the vegetable proteins 

 to-day are in general easier of access for 



' These and related questions are discussed in 

 detail by Mendel, "Ergebnisse der Physiologie, " 

 1912, XI. 



chemical investigation and isolation than the 

 related compounds of animal origin. And it 

 is this fact which encouraged us to undertake 

 what Carl Voit long ago proclaimed as the 

 ideal method, viz., the feeding of isolated food- 

 stuffs under controllable conditions. The la- 

 borious and costly investigations which are 

 under way have been made possible by the 

 cooperation of the Carnegie Institution of 

 Washington. A detailed report of the first 

 two years' work and the literature pertaining 

 thereto is available in Publication 156, Parts 

 I. and II., of the Carnegie Institution." The 

 following pages are intended to call attention 

 very briefly to some aspects of these studies. 



We have undertaken to investigate certain 

 features of nutrition by feeding isolated food 

 substances to albino rats. The selection of 

 this animal has been determined by several in 

 part obvious considerations. The white rat is 

 easily reared and cared for. Its small size 

 reduces the food requirement to a magnitude 

 which falls within the range of experimental 

 possibility where the preparation of special 

 dietaries by laborious processes is a funda- 

 mental prerequisite. Furthermore, the longev- 

 ity of this animal is, according to Donaldson, 

 about three years; so that the first year of life 

 corresponds to a long span in terms of human 

 years. Not insignificant is the additional fact 

 that the white rat has in recent years been 

 made the subject of exceptionally extensive 

 measurements in respect to growth and vari- 

 ous features of development at the Wistar 

 Institute in Philadelphia. In this way phys- 

 ical standards, so to speak, have been estab- 

 lished for this animal. 



At the outset numerous problems of experi- 

 mentation have arisen quite apart from the 

 main question itself. Can rats be kept in 

 health indefinitely under cage conditions which 

 permit the control of the food intake and col- 

 lection of the excreta? For the description of 

 the cages and experimental technique we must 



' ' ' Feeding Experiments with Isolated Food- 

 substances, " by Thomas B. Osborne and Lafay- 

 ette B. Mendel, with the cooperation of Edna L. 

 Ferry, Carnegie Institution of Washington, Publi- 

 cation 156, Parts I. and II., 1911. 



