1891.] 



Phenomena of Human Respiration. 



109 



samples from the bag and other two bell-jars were treated in the same 

 way. The next day the barium carbonate had subsided, and the clear 

 fluid was titrated according to Pettenkofer's method. The reductions 

 to dryness, to and 760 mm., were speedily made with the help of 

 the table I have given in the paper previously referred to. 



Let us now follow the changes occasioned by the re-breathing of 

 35 litres of air for a period of 5 minutes ; there were a few additional 

 seconds included, as the re-breathing had to be stopped at the end of 

 an expiration, which of course might not exactly correspond with a 

 lapse of five minutes. The following are the mean percentages of 

 C0 3 contained in the bell-jar after its air had been re-breathed : 



Myself. after 5 m. 2 sec. 3'42 per cent C0 2 . 



Mr. Russell 5m. 4 sec. 3'87 



Mr. Hoskins ,, 5 m. 10 sec. 3'44 ,, 



W. Alderwood ,, 5 m. 5 sec. 3*29 ,, 



consequently in every case the air was becoming considerably 

 vitiated ; yet it was only in the last minute that an unpleasant sensa- 

 tion, if any, was felt. 



If we compare the amount of carbonic acid expired by re-breathing 

 35 litres of air for five minutes with the amount of carbonic acid 

 which would have been expired in the same time in ordinary breath- 

 ing, we find invariably less C0 2 in the re-breathed air than in rormal 

 respiration ; this is shown clearly in the following table, in which the 

 C0 2 expired in ordinary breathing has been calculated for the time 

 taken in the re-breathing stage of the experiment. 



It follows that there is always less carbonic acid expired in a given 

 time when air is re-breathed than in ordinary breathing. In the 

 present experiments the mean proportions varied for four different 

 persons between 1 to 1-041 and 1 to V221 ; or, in other words, a 

 mean of 9*3 per cent, carbonic acid which would have been expired 

 in a certain time in ordinary breathing is found to have disappeared 

 in 35 litres of air re-breathed during the same time. 



I 2 



