30 A BIOMETRIC STUDY OF BASAL METABOLISM IN MAN. 



of us. All of the operators acquired their technique personally in the 

 Nutrition Laboratory. The data are, therefore, due not merely to 

 uniform method and apparatus but to comparable manipulation 

 throughout. 



The routine involved the appearance of the subjects at the Labora- 

 tory at about 8 a. m., in the post-absorptive condition, i.e., about 12 

 hours after taking their last food. They then lay down upon a couch 

 or bed and remained perfectly quiet, usually half an hour prior to the 

 first period. Absence of muscular activity during the experimental 

 periods was assured by the bed being provided with a graphic registering 

 device which indicated the slightest alteration in the change of position 

 of the center of gravity of the body, or by the attachment of a chest 

 or thigh pneumograph which registered slight muscular movement. 



Experiments were usually made in several periods of 15 minutes, 

 with interims of 15 to 20 minutes. To secure the most representative 

 value possible, experiments were usually made two, and frequently 

 many more, days with the same subject. 



The pulse was nearly always taken, and usually the oral tempera- 

 ture. Subjects with febrile temperature were rejected. 



In selecting the periods of observation to be used, those in which 

 there was an absence of muscular activity were chosen. This was 

 assured by having the individual under observation lie on a bed, one 

 side of which rested on a knife edge while the other was supported by 

 a spiral spring. A change in the level of the bed altered the tension 

 of a pneumograph connected with a tambour and kymograph. The 

 smallest motion of any kind, even a movement so slight as to be 

 imperceptible to the observant trained nurse, disturbed the linearity 

 of the kymograph record. Thus periods of perfect muscular repose 

 could be selected on the basis of an instrumental record alone, without 

 the possibility of the personal equation of the observer playing any part. 



In the respiration calorimeter, in which each experiment lasted at 

 least 1J/2 hours, such complete muscular repose could not be obtained 

 as in the shorter periods with the universal respiration apparatus. But 

 here the subjects fully understood the necessity for quiet, and while 

 the kymograph records naturally show somewhat greater irregularity 

 in the long than in the selected short periods, the subjects were remark- 

 ably quiet and the irregularities in the tracings are so slight as to indi- 

 cate negligible muscular activity. 



The computation of heat-production is usually based upon the 

 oxygen consumption, making allowances for the slight changes in the 

 calorific equivalent of oxygen with varying respiratory quotients. The 

 calorific value of oxygen is much more nearly constant, irrespective of 

 the character of the katabolism, than is that of carbon dioxide, and 

 hence in practically all of the cases we have used the oxygen consump- 

 tion. In a few instances where the oxygen determinations were faulty, 



