30 president's address. 



that the issuing stream of the breath swept the tube free from con. 

 tained air, at any rate in the portion from which samples would 

 be taken. These showed that a stream issuing with the velocity 

 of the air in a quick, forcible expiration sweeps out the gaseous 

 contents of the tube in such a complete manner that it would 

 appear as if the issuing stream pushed the air already in the 

 tube in front of it. 



Two sets of the results obtained in the Physiological Labora- 

 tory have been published by Miss E. Pinkerton in the Proceed- 

 ings of this Society. In the first series, estimations were made 

 only of the amount of carbon dioxide, while in the second series 

 the percentage of oxygen was also measured. In the first series, 

 the conclusion was reached that analysis of the last 625 c.cm. of 

 expired air shows that the difference in percentage of carbon 

 dioxide in any portion of it, does not exceed the error in the 

 analytical method when the expulsion is performed within two 

 seconds for amounts of two litres and over, and within one 

 second for quantities of one or two litres of expired air. When 

 the air is expelled more slowly, the successive portions of expired 

 air continue to show higher percentages of carbon dioxide. The 

 error in the analytical method was such that there might be an 

 error as great as - 2% in the calculated percentage of carbon 

 dioxide, though the duplicates all yielded figures lying within 

 0-1% in the calculated percentage. In the second series, more 

 accurate methods for estimating carbon dioxide were used, so 

 that attention could be paid to the figure in the second decimal 

 place. The oxygen estimations were of corresponding accuracy. 

 With the greater accuracy, it became quite evident that there 

 is a slow rate of change in the last part of the expired air. This 

 change does not amount to more than 0'22/' in the last 625c. cm. 

 expired in the case of carbon dioxide, and to more than - 36% 

 in the case of oxygen. The amount of alteration is dependent 

 on the speed with which the air is driven from the lungs. These 

 results are of great importance, since they make it clear that 

 the air remaining in the air-passages at the end of an expiration 

 will contain more carbon dioxide than that which has been 

 expelled through the nose and mouth. 



