APPARATUS AND TECHNIQUE USED IN PRESENT STUDY. 13 



it was made a fundamental principle of this investigation that the 

 experiments with the two forms of apparatus selected for comparison 

 should be carried out with the same subject and as nearly simultane- 

 ously as possible. While of course it was impossible to determine the 

 respiratory exchange on the same subject with two apparatus at the 

 same time, it was believed that by using the method of alternation 

 on the same day the influence of sequence could be eliminated; fur- 

 thermore, if a large number of comparisons were made with any two 

 respiration apparatus, the multiplicity of results would eliminate any 

 differences due to the individuality of the subject. Unfortunately the 

 number of subjects used for many of the comparisons is not so large 

 as would have been desirable, and also the same subjects were not used 

 for all of the comparisons. This was due to the period (several years) 

 over which the investigation was continued and the difficulty of being 

 able to keep the subjects available for any great length of time. 



Granting all these conditions are met, there still remains the question 

 of a suitable base-line or standard. Given two sets of results with two 

 forms of respiration apparatus, unless we know which is correct we 

 have no way of assigning a value to the comparison. Unfortunately, 

 we have no simple and accurate method of measuring normal respi- 

 ration. The only apparatus which is at present available is the body 

 plethysmograph used by Haldane and Priestley. 1 The difficulties of 

 getting an air-tight closure around the neck and of maintaining suitable 

 temperature conditions must be very great with this apparatus, and 

 it seems hardly practicable to attempt the measurement of the respi- 

 ration volume under these conditions with any large number of subjects. 



Investigations extending over several years have led us to believe 

 that the respiration of a man inclosed in a respiration calorimeter, but 

 free to move, is perfectly normal, for in such a chamber a subject may 

 place himself in a perfectly comfortable position. The bed calorimeter 2 

 of the Nutrition Laboratory permits measuring, with a high degree of 

 accuracy and in periods of 3 hours or more, the respiratory exchange 

 of a man in a reclining position. On the basis that the respiratory 

 exchange is normal in the bed calorimeter, the results obtained with it 

 have been compared with those obtained with the Benedict universal 

 respiration apparatus; this apparatus has, in turn, been compared with 

 others and modifications of the apparatus and conditions compared 

 with each other. 



Still another element in the whole question of comparable conditions 

 has to be carefully considered, i. e., the elimination of external muscu- 

 lar activity. In several publications from this laboratory 3 the impor- 



'Haldane and Priestly, Journ. Physiol., 1905, 32, p. 242. 

 2 Benedict and Carpenter, Carnegie Inst. Wash. Pub. 123, 1910. 



3 Benedict and Talbot, Am. Journ. Diseases of Children, 1912, 4, p. 130; Benedict, Deutsch 

 Archiv f. klin. Med., 1912, 107, p. 158. 



