CRITICAL DISCUSSION OF RESPIRATION APPARATUS. 261 



which are prescribed in the manipulation of each type of apparatus. 

 He must assure himself that the apparatus is in perfect condition and 

 must control it frequently in order that he may depend upon his results. 

 For example, if he is working with a closed-circuit apparatus, he must 

 be perfectly sure that the apparatus is air-tight and will remain air-tight 

 throughout the experimental period; also that the various absorption 

 apparatus are functionating perfectly. If the method involves meas- 

 urement Avith spirometers and gas analysis, these must be controlled 

 so far as possible, the spirometers by calibration and the gas analyses 

 by frequent comparisons with analyses of outdoor air. 



As many controls as possible should also be used for the subject. 

 Records of the pulse-rate, respiration-rate, and some graphic registra- 

 tion of the degree of repose should be obtained. In addition, data 

 should be recorded as to his general condition, his previous condition, 

 and any factors which may influence the respiration during the experi- 

 ment, particularly those of a psychical nature. 



Every precaution should be taken that the conditions under which 

 the experiments are made are favorable to uniformity in results. For 

 instance, the experiments should be made in a perfectly quiet room, 

 where no interruptions will be likely to occur. It has been frequently 

 observed in this laboratory that the unexpected and unnecessary 

 entrance of a person into the room during an experiment has resulted in 

 a very noticeable change in the pulse-rate and a consequent change in 

 the metabolism. Sudden noises or sudden disturbances also result in 

 variable values, particularly if the subjects are new and unaccustomed 

 to the laboratory. Also, so far as possible, the manipulation of the 

 apparatus should not be visible to the subject. With the Benedict 

 apparatus it has been our custom to conceal the whole apparatus with 

 a curtain in such a way that the subject can not see the spirometer 

 moving, the valve turned, or any of the other operations connected 

 with the progress of the experiment. In the use of the Tissot spirome- 

 ter, it is desirable to place the spirometer behind the subject so that 

 he can not see it rising as he exhales. Some subjects have had the idea 

 that the object of the experiment was to fill the spirometer as rapidly 

 as possible; obviously good results can not be obtained with these 

 subjects. 



If a subject is quiet, the pulse-rate is constant, and the apparatus 

 is in good working condition, the values of the carbon dioxide and the 

 oxygen obtained in three succeeding experimental periods should not 

 vary more than 5 per cent. It has been the custom in this laboratory 

 to expect results within 10 c.c. per minute for both the carbon-dioxide 

 elimination and the oxygen consumption; even more closely agreeing 

 results may be obtained. 



. It is rather difficult to state what the differences in the total metabo- 

 lism of an individual may be from day to day. Magnus-Levy 1 has cited 



'Magnus-Levy, Zeitschr. f. klin. Med., 1897, 33, p. 258. 



