DEVELOPMENT OF NUTKITION INVESTIGATIONS, 455 



In the earlier years of the nutrition investigations many analyses 

 of American food materials were made, as the data regarding the 

 f'hemical composition of such food materials were comparatively 

 limited. Information along this line has, however, accumulated very 

 rapidly as a result of studies carried on by diti'erent investigators, 

 and data are now so abundant that studies of proximate composi- 

 tion of food materials no longer constitute one of the lines of work 

 followed in the cooperative nutrition investigations of the office. 

 Dietary studies — that is, studies of the kinds and amount of food 

 l^urchased, eaten, and wasted — were early recognized as of great 

 importance, and a large number have been made in private families, 

 schools, colleges, public institutions, and elsewhere, under a variety 

 of conditions and in widely separated regions. 



No matter what its composition, food is of no use to the body unless 

 it is digested, and it is natural that experiments should have been 

 undertaken with a variety of food materials to leai-n how thoroughly 

 they were assimilated by the body and to ascertain the effect of 

 various methods of preparation and combination upon thoroughness 

 of digestion. Furthermore, it is supposable that the occupation in 

 which the subject is engaged, whether active or sedentary, may have 

 an influence upon the work of the digestive tract, and this question 

 has also been studied. Many questions regarding the thoroughness 

 of assimilation may be investigated with the aid of ferments under 

 conditions which approximate those in the body, and a large number 

 of such artificial digestion experiments have been carried on, particu- 

 larly in studying the ease and rapidity of digestion, a question which 

 is very different from thoroughness of digestion, though the two are 

 often confused in popular discussions of the subject. 



Variations in the excretion of nitrogen have long been regarded 

 as indications of changes taking place in the body, and it has been a 

 general custom of physiologists to study the balance of income and 

 outgo of nitrogen. Such studies have formed a part of the nutrition 

 investigations of the department. Much more useful as a means of 

 studying the food requirements of the body and other questions are 

 determinations of the balance of carbon, oxygen, and hydrogen, as 

 well as nitrogen, and determinations of the balance of income and 

 outgo of energ}'. Such studies necessitate special apparatus, and the 

 respiration calorimeter already referred to has proved itself admir- 

 ably adapted to this purpose, and it seems fair to say that it is so far 

 the most perfect instrument of its type. The respiration calorimeter 

 is of such a size that a man may remain in comparative comfort in the 

 respiration chamber for a number of hours or days, and the measure- 

 ments of income and outgo of matter and energy may be made with 

 great accuracy. The determination of energy values of food and 



