72 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



of a single food or pure food substance were given. Accordingly, the 

 most of our experiments were made with relatively small amounts 

 of food, with a correspondingly small fuel value, this fuel value occa- 

 sionally representing but one-half or two-thirds of the daily needs. 

 It was only when the period was somewhat curtailed and the observa- 

 tions confined to the night period that satisfactory base-lines could be 

 obtained and the effect of the superimposed food definitely determined 

 without the disturbing factor of the depression due to fasting. This 

 latter plan of experimentation leads us naturally into the subdivision 

 of the experimental day and a complete abandonment of the 24-hour 

 method of experimenting. 



From the foregoing considerations the only conclusion that can be 

 reached is that the 24-hour period does not lend itself to a sharply 

 defined study of the influence upon metabolism of the ingestion of 

 food first, because the establishment of a suitable basal value is 

 extremely difficult, since each day of fasting shows a lowered metabolism 

 as the specific result of the fasting; and second, because it has been proved 

 physiologically impossible for many subjects, after two days of fasting, 

 to take large amounts of food. These large amounts are particularly 

 desirable for studying the influence upon the metabolism of a special 

 food substance, especially as the increment, which is frequently slight, 

 must be included in the total measurements for the 24-hour period 

 and would thus in some cases, either wholly or in part, escape obser- 

 vation. This plan of experimentation thus defeats its own end, 

 minimizing the effect of the food ingestion by a physiological reaction 

 of the subject after fasting, and attenuating the frequently small incre- 

 ment in the metabolism due to the stimulating action of the food 

 materials. 



EXPERIMENTS OF APPROXIMATELY 8 HOURS. 



The unsatisfactory termination of the attempts to use the 24-hour 

 period in studying the influence of the ingestion of food upon metabo- 

 lism led to a rearrangement of the experimental plans and the substi- 

 tution of shorter experiments in which the metabolism was studied 

 during that section of the digestive cycle when the maximum digestive 

 activity would normally be expected. The experimental period would 

 thus begin at approximately 9 o'clock in the morning and continue 

 for about 8 hours. 



CRITIQUE OF 8-HOUR METHOD. 



In the 8-hour periods it was easier for the subject to follow a pre- 

 scribed routine, such as sitting quietly in a chair without major muscu- 

 lar movement, than in the 24-hour periods. Furthermore, the uncer- 

 tainty as to the length of time the subject slept was usually eliminated, 



