352 



RESPIRATION. 



gas, when the body is in a state of rest, be 

 able to determine both the relative and the 

 absolute quantity of carbonic acid gas in the 

 expired air from the number of respirations 

 alone, when these are either increased above, or 

 diminished below the normal number, provided 

 the bulk of each respiration continues equal. 

 He has constructed the following table to 

 illustrate the variations in the absolute quan- 

 tity of carbonic acid gas occasioned by altera- 

 tions in the frequency of the respiratory move- 

 ments. The normal number of respirations is 

 supposed to be 12, the average bulk of each 

 respiration to be 500 cubic centimetres (30'5 

 English cubic inches), and the percentage 

 of carbonic acid to be 4*1. 



Bulk of the air expired. The quantity of 

 air thrown out of the lungs at each expiration 

 has also an influence upon the percentage 

 and absolute quantity of carbonic acid gas in 

 the expired air. Vierordt, in six experiments, 

 found that while the average of carbonic acid 

 gas in the expired air in a normal expiration 

 in a state of rest was 4*78 per cent., in the 

 deepest expiration he could make, it was 4'05 

 per cent. 



The stoppage of the respiratory movements 

 for a time has also a marked effect upon the 

 quantity of carbonic acid in the expired air. 

 Vierordt has made four series of experiments 

 upon himself to ascertain the extent of this 

 influence upon the quantity of carbonic acid 

 evolved from the lungs. In the first series he 

 shut his mouth and held his nose from 20 to 

 60 seconds (the longest period he could con- 

 tinue the experiment), and then made the 

 deepest possible expiration. In the second 

 series he made the deepest inspiration pos- 

 sible, then suspended the respiratory move- 

 ment for a longer or shorter time, at the ter- 

 mination of which he made the deepest ex- 

 piration. This experiment he was able to 

 prolong to 70, 90, and even 100 seconds. In 

 the third series he made an ordinary inspira- 

 tion before suspending the respiratory move- 

 ments, and after this suspension had con- 

 tinued for different periods up to 30 seconds, 



he made an ordinary expiration. The fourth 

 series of experiments was to ascertain the 

 period of time after the stoppage of the respi- 

 ratory movements when the percentage of 

 carbonic acid gas becomes uniform in the 

 different parts of the lungs and air passages, 

 and this he found took place after 40 seconds. 

 He has arranged the results of the three first 

 series of experiments in several tables, ex- 

 hibiting the difference between the percentage 

 and absolute quantity of carbonic acid gas in 

 the expired air at various periods, after the 

 suspension of the respiratory movements 

 under the circumstances mentioned, and when 

 the respiratory movements proceed in the 

 normal manner. In the first series of ex- 

 periments, the percentage of the carbonic 

 acid in the expired air, after the respiratory 

 movements had been suspended 20 seconds, 

 was higher by 1'73 than when these move- 

 ments were normal, but the absolute quantity 

 evolved from the lungs had diminished by 

 2'642 English cubic inches, and at the end of 

 55 seconds its percentage had increased 2'32, 

 but its absolute quantity had diminished to 

 the extent of 12*382 cubic inches. In the 

 second series of experiments, where the deep- 

 est possible inspiration preceded, and the 

 deepest possible expiration followed, the sus- 

 pension of the respiratory movements, the 

 absolute quantity of carbonic acid gas evolved 

 from the lungs, for the first 15 seconds, was 

 somewhat more than what would have oc- 

 curred had these movements proceeded in 

 the normal manner, but after this it began to 

 diminish ; and when the respiratory move- 

 ments had been suspended for 95 seconds, it 

 was diminished to the extent of 14'078 

 English cubic inches, though its percen- 

 tage had considerably increased. At the end 

 of the 100 seconds, the percentage of the 

 expired air was 3'08 above the normal quan- 

 tity in ordinary respiration. In the- third 

 series of experiments, the carbonic acid in the 

 expired air, at the end of 30 seconds, was 1*55 

 ptr cent, above the normal quantity. These 

 experiments prove, therefore, that when the 

 respiratory movements have been suspended 

 for a time, the percentage of carbonic acid in 

 the expired air will increase, but the absolute 

 quantity evolved from the lungs will be 

 diminished, so that the increase in the per- 

 centage of this gas does not by any means 

 compensate for the diminished quantify of air 

 passing through the lungs. 



When the same air is breathed more than 

 once, the quantity of carbonic acid in it is 

 increased. Allen and Pepys * state that air, 

 passed 9 or 10 times through the lungs, con- 

 tained 9 5 per cent, of carbonic acid gas ; and 

 the greatest quantity obtained, m air breathed 

 as often as possible, was 10 per cent. Mr. 

 Coathupe f found the average quantiu of 

 carbonic acid gas, in air in which warm- 

 blooded animals had been confined until they 

 were becoming comatose, to be ]0'42 per 



* Philos. Transact, of London for 1808. 

 f Opus cit. 



