354 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



Control of external muscular activity. It has been repeatedly stated in 

 publications from this Laboratory 1 that, in any study of metabolism in which 

 comparable results are to be obtained, it is necessary to have as nearly as 

 possible complete muscular repose and that there must be a graphic record 

 which will indicate that such repose has been maintained throughout the 

 periods of the experiments which are compared with each other. Such a 

 graphic record may be obtained either by means of pneumographs around 

 the thighs and thorax or by means of a pneumograph or pneumatic bulb con- 

 nected to the bed support. If these devices are connected with a sensitive 

 recording tambour, the slightest muscular movement of the subject results 

 in a change in the volume of the air in the pneumograph, which is immediately 

 recorded by the pointer of the tambour upon the smoked surface of the rotat- 

 ing drum of a kymograph. 



In addition to the record of the amount of complete external muscular repose 

 it is equally important to note any drowsiness or sleep which may occur during 

 the measurement of the metabolism. Recent experience with human subjects 

 in a series of experiments upon the metabolic effect of the ingestion of alcohol 

 has shown that the degree of wakefulness can be satisfactorily recorded by 

 having the subject press a push button periodically in response to a stimulus. 

 The stimulus is supplied by a signal magnet which is operated once every half 

 minute. The magnet is so placed that the subject can hear it readily and is 

 in series with a battery, clock, and second signal magnet which records upon 

 a moving kymograph drum. The push button operated by the subject is 

 connected with a battery and an independent recording signal magnet, thus 

 giving a record of the response to the signal. A continuous record of responses 

 gives positive evidence of wakefulness on the part of the subject, while a 

 continuous lack of responses is indicative of drowsiness or actual sleep. 



The effect of external muscular activity is to change the total metabolism, 

 while the effect of drowsiness or sleep is to change the apparent character of 

 the respiratory exchange; accordingly, a graphic record of both is essential for 

 a reliable interpretation of the results obtained. 



Length of periods. The length of the periods of observation is naturally 

 dependent upon the total effect to be measured and upon the apparatus used. 

 When the effect is exceedingly small, and particularly when the peak effect 

 and its time relation are desired, it is essential to make the periods as short as 

 possible, preferably 10 to 15 minutes. If an apparatus with a closed chamber 

 is used, periods as short as these are not possible; with such an apparatus, 

 periods of at least 30 minutes should be employed and 45-minute periods are 

 more reliable. 



Apparatus. From the experience of the last 12 years in studies of this 

 character, we have come to the conclusion that some form of respiration 

 apparatus is desirable with which it is possible to measure the gaseous exchange 

 continuously in short periods. At present the best combination for this 

 purpose with a trained subject is found to consist of a face mask, valves for 

 separating inspired and expired air, two spirometers (preferably of the Tissot 

 type), and a Haldane portable gas-analysis apparatus for analyzing the 

 expired air. The face mask is one used in the Siebe-Gorman mine-rescue 

 apparatus. 2 To secure reliable results, the tightness of the mask against the 

 face must be assured. The valves for separating inspired and expired air most 

 used in this laboratory are the Thiry-Tissot model, 3 but any valve which is 



Benedict, Deutach. Arch. f. klin. Med., 1912, 107, p. 156; Benedict and Talbot, Carnegie Inst. 

 Wash. Pub. No. 201, 1914, pp. 31 and 59; Benedict, Carnegie Inst. Wash. Pub. No. 203, 1915, p. 311. 



"This may be obtained from H. N. Elmer, 1140 Monadnock Building, Chicago, 111. 



3 Both the Thiry-Tissot valves and Tissot spirometer were obtained from Pirard and Coeurde- 

 vaoho, 7 rue Blainville, Paris, France. 



