490 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



air per millimeter of carbon-dioxide tension. To say that this means 

 a change in irritabihty of the respiratory center would seem to imply 

 that if there is a change in any of the factors of respiration, such as 

 respiration rate, dead space, carbon-dioxide elimination, and total 

 ventilation, the irritability would be also changed. So that when 

 we say that the irritabihty of the respiratory center is decreased with 

 these subjects, it is only in the sense that Loewy and Zuntz use the 

 term. 



The general conclusions from the study of the mechanics of respira- 

 tion and particularly the alveolar air for the subjects in our research 

 are that the low diet produces a distinctly lower respiratory activity, 

 and although the alveolar carbon dioxide remains essentially con- 

 stant, there is a definite tendency toward a lessened work of ventila- 

 tion, with a decreased sensitivity of the respiratory center. The corre- 

 lation of this finding with the total metabolism must be noted in subse- 

 quent discussion. The general lowering of the metabolism shown calls 

 for a lower ventilation of the lungs for the removal of carbon dioxide 

 and hence the work of ventilation is less. 



Subsidiary evidence regarding the reasonable constancy in the 

 alveolar carbon dioxide is supphed by the fact that the alveolar carbon 

 dioxide with Pea was directly determined before a cross-country run 

 on November 28 and found to be 48.4 mm.; immediately after the 

 cross-country run, which was 6| miles (10.9 km.), it was found to be 

 42.9 mm. The respiration rate under these conditions was, as found 

 from kymograph records, 18.3 respirations per minute prior to the 

 run and 23.3 respirations subsequent to the run, although it was im- 

 possible to adjust the apparatus and get a record until some little 

 time had elapsed after the completion of the run. 



GASEOUS METABOLISM DURING REST. (INDIRECT CALORIMETRY.) 



Although the body-weight over considerable periods of time may 

 properly be taken as an index of nutritional level, or at least of varia- 

 tions in nutritional level, it of itself gives no idea as to the exact 

 caloric requirements. It seemed imperative, therefore, to measure 

 quantitatively the caloric output of these men at the different nutri- 

 tional or different weight-levels. The ideal apparatus for measuring 

 the caloric output is the respiration calorimeter, but its use was pre- 

 cluded, first, on account of the impossibility of transporting this com- 

 phcated apparatus to Springfield, and second, because of the length of 

 time required for the several experiments. Consequently the de- 

 termination of the gaseous exchange as frequently as possible through- 

 out the entire period of dietetic control seemed to be the best method 

 for obtaining information regarding the caloric requirements. 



As stated in the chapter on technique (see p. 82), the gaseous 

 metaboUsm of nine of the men was determined nearly every morning 



