I.— PHYSIOLOGY 



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order to improve the mixing may contain two horizontal layers of copper 

 gauze, one just above the opening of the delivery tube and the second 

 towards the top of the bottle below the exit tube. Samples of the mixed 

 air as it leaves the bottle are analysed every five minutes by means of a 

 Haldane gas analysis apparatus fitted with a 10 c.c. burette (a 30 c.c. 

 burette has recently been used), connected to the bottle by means of lead 

 tubing of fine bore. The expired air then passes to a large gas meter 

 measuring 15 litres per revolution, which is read every five minutes. 

 A rubber anaesthetic bag is connected by means of a T-piece to the tube 

 between the bottle and the meter. With a large meter and bag in circuit 

 there is no perceptible resistance to ordinary breathing, and the valves 

 have been constructed with the same end in view. They consist of Paul's 

 rubber intestinal tubing split longitudinally along both edges and clipped 

 at intervals of about an inch with clips. Dr. Alice E. B. Harding, who 

 has used the method for children, has found that a practical method of 

 testing for leaks between the face and the mask is to hold a polished metal 

 spatula near the junction ; if expired air escapes the surface of the metal 

 is dimmed by the deposition of moisture. Five consecutive experiments 

 are given in the table. They were usually continued for 25 minutes or 



half an hour, though a shorter period might sometimes be enough. 

 Contrary to the general impression the carbon dioxide after the first five 

 or ten minutes gives very constant results, if the patient is quiet and 

 comfortable. An increase towards the end of the period can usually be 

 accounted for by some extraneous factor, such as shivering or restlessness. 

 There is no necessity for the examination to be restricted to the nursing 

 home or hospital ; but the patient should be advised to do the minimum 

 of walking on the morning of the test. Most of the original experiments 

 were carried out under these conditions. 



The advantage of this method is that the constancy of the breathing 

 and metabolism throughout the period can be assessed ; its disadvantage 

 is that the total volume of expired air is not collected before taking out 



