264 COMPARISONS OF RESPIRATORY EXCHANGE. 



quotients are much more difficult to obtain than accurate figures for 

 the carbon-dioxide elimination and oxygen absorption. 



The uniformity of results is also greatly dependent upon the amount 

 of training which the subject has had. In general, one can not expect 

 so good results from untrained subjects, particularly if they are patho- 

 logical, as from trained subjects. This is generally true, regardless 

 of the apparatus which is used. With no known respiration apparatus 

 can an investigator be absolutely certain that the results obtained in a 

 first experiment with a subject will be accurate. Magnus-Levy 1 has 

 stated that in one case it was necessary for him to make experiments 

 with one subject daily for over 10 days before he was certain that there 

 was not a slight diminished metabolism due to the lack of training. 



In drawing conclusions, the results obtained must be very carefully 

 examined and the different factors involved compared. For example, 

 the values for the carbon-dioxide elimination should be compared with 

 the values for the total ventilation and those for the total ventilation 

 with the respiration-rate. Records of the pulse-rate and respiration- 

 rate are of great importance, and valuable evidence as to the character 

 of the respiration may be secured from graphic records. An idea of 

 the character of the experiment may also be obtained from readings of 

 the ventilation from minute to minute, which may be secured from the 

 movements of the spirometer on the Benedict respiration apparatus 

 or from the meter with the Zuntz-Geppert apparatus. 



The condition of the subject at the time of the experiment must also 

 be considered very carefully. For example, the results obtained in 

 an experimental period which follows immediately after the subject 

 has lain down upon the couch can not be expected to be comparable 

 with those obtained in the experimental periods following or carried out 

 some time later. A subject should rest quietly upon the couch for 

 at least a half hour, preferably three-quarters of an hour, before the 

 beginning of the experiment, unless a study is being made of the effect 

 of the previous state upon the metabolism. In such a study, however, 

 the same character of results would not be expected as would be ob- 

 tained when experiments were being made for the purpose of establish- 

 ing basal values for future work. In determining a base-line for later 

 investigations, extreme care is necessary in the interpretation of results. 

 Furthermore, as uniform results as possible should be secured, other- 

 wise if a very small increase is superimposed upon a variable base-line 

 there is no definite evidence that the increase is positive. 



In general, when interpreting the results of experiments, one must 

 distinguish between the variations due to the apparatus and variations 

 due to the subject. The first can be eliminated within certain limits 

 and these limits must be determined for each of the apparatus used. 



^lagnus-Levy, Zeitschr. f. klin. Med., 1897, 33, p. 258. 



