546 JOHN R MURLIN 



is to be determined. The subject comes to the laboratory early in the 

 morning after having taken a very light breakfast of black coffee and 

 toast, or no breakfast at all. For half an hour the subject is required to 

 lie perfectly still wearing the nose clip and breathing through the mouth- 

 piece into the room air or breathing through the face mask into the room 

 air. He thus becomes accustomed to all the sensations incident to the 

 experiment A slight pulsation of the air current transmitted from the 

 blower is felt by the patient unless special means is taken to muffle it. 

 Such vibrations may become very annoying to the subject. 



When the absorbers have been weighed and the patient has become 

 sufficiently composed the blower is started and the apparatus is run idle 

 blowing the air round and round through the circuit for at least two min- 

 utes in order to make certain that any carbon dioxid left over from a 

 previous observation shall have been completely removed. With a small 

 weight placed upon the spirometer this preliminary run serves also to 

 test the entire circuit for tightness. If after a minute or two the spirom- 

 eter holds its level the entire circuit is air tight and the experiment 

 may proceed. The oxygen meter is read at this point. 



With an intelligent subject it is our custom to let the subject turn the 

 valve himself, instructing him to do so just before beginning an inspira- 

 tion. With a .subject wholly unaccustomed to the apparatus or not suffi- 

 ciently intelligent to understand what is meant by "respiratory pause" 

 the observer quickly turns the valve at the moment of respiratory 

 rest intervening between the end of an expiration and the beginning of an 

 inspiration. In either case the second hand of a watch is read at the in- 

 stant the valve is thrown. If the air current is passed through a moisten- 

 ing bottle which follows the acid absorber in the carbon dioxid train the 

 air comes to the subject feeling rather soft with moisture, and also feel- 

 ing perhaps a little cool from the temperature of the water. These are 

 the only sensations which the subject should experience, when the valve 

 is thrown connecting him with the circuit. There should be no trace of 

 irritation either from the air itself or from the apparatus connecting 

 with his face. 



With a little experience oxygen can be fed in through the meter at ap- 

 proximately the rate at which it is absorbed by the subject. This method 

 is preferable in the writer's opinion to the intermittent feeding of oxygen, 

 providing only that the rate of flow be kept low enough so that at the ter- 

 mination of the observational period the spirometer shall be lower than 

 it was at the moment the valve was first thrown. It is far more important 

 to terminate the observation correctly with reference to the phase of res- 

 piration when the valve is thrown than it is to terminate the observation 

 on the second by the watch. The observer, therefore, gives his entire at- 

 tention to throwing the valve and only notices the position of the second 

 hand after he has successfully thrown the valve. The blower is allowed 



