54 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



Theoretically the measurement of the basal value during a 24-hour 

 fast, to be immediately followed by a day in which the prescribed food 

 intake is given, is an ideal method for studying the influence of the 

 ingestion of food, inasmuch as it includes the activities of a complete 

 normal day. The subject is thus awake during the major part of the 

 24-hour period and asleep the normal time, the movements being 

 restricted to those possible inside a respiration chamber, such as dress- 

 ing and undressing, drinking water, telephoning, urinating, and similar 

 activities. By means of the program prepared for the subject, this 

 daily cycle of normal activity could be approximately duplicated in 

 comparison experiments without difficulty. In some respects the 

 longer periods are pleasanter for the subject, as more freedom is allow- 

 able in the routine and strict muscular repose is not necessary. 



As the total amounts of carbon dioxide given off and oxygen con- 

 sumed are relatively large in a 24-hour experiment, the experimental 

 errors are practically eliminated; the chemical and physical measure- 

 ments thus have a greater degree of manipulative accuracy than is the 

 case in short periods. 



Furthermore, the continuance of food experiments for 24 hours 

 insures a complete measurement of the effect of food, especially with 

 certain diets, for undoubtedly the influence lasts at times longer than 

 the 12 hours usually assumed to establish post-absorptive conditions. 

 Finally, the long-period experiment allows the ingestion of food at the 

 regular times of the day and in the regular amounts, thus permitting 

 a summation effect and the obtaining of information as to the influence 

 of the diet upon the basal metabolism for the whole day. 



On the other hand, the 24-hour period can not give a minimum 

 metabolism value for the subject, since it necessarily includes so much 

 extraneous muscular activity. Although the method used to secure 

 comparable activity in the experiments was as satisfactory as was then 

 possible, it could give only an approximate control, with no assurance 

 of perfect uniformity. Ocular evidence of the activity is at best more 

 or less unreliable, as observers vary widely in their estimates of the 

 quantitative relationships of various minor muscular movements. 



The 24-hour type of experiment has yet another disadvantage, for 

 although the deprivation of food for 24 hours is by no means so great 

 a hardship as would ordinarily be supposed, yet the enforced abstinence 

 from food for this length of time is not borne so cheerfully by the ma- 

 jority of individuals as is the short-period fasting. 



Again, the 24-hour period gives no information as to the time rela- 

 tions or the maximum effect following the ingestion of food. We are 

 thus unable to tell from the results whether the increase extends over a 

 long period or whether there is a sharp rise and fall in metabolism, 

 i. e., a "peak" effect. Nor does it take into consideration the remote 

 possibility of a compensation that is, a subsequent lowering of metab- 



