RESPIRATION. 543 



similar results. Before the section the blood in the crural vein contained 9.5 

 per cent, of O and 60 per cent, of CO 2 ; after section it contained 13.5 per 

 cent, of O and 40 per cent, of CO 2 , showing that the consumption of O by 

 the tissues and the formation of CO 2 were considerably lessened. After de- 

 struction of the spinal cord respiratory activity falls to a minimum. 



The study of the effects of alterations in the composition of the inspired air 

 on the absorption of O and the elimination of CO 2 are of great importance. 

 Nitrogen is merely a mechanical diluent of the inspired air, and may be 

 replaced by H or by other inert gas, so that alterations in its percentage do 

 not, per se, affect the respiratory phenomena ; but changes in the percentages 

 of O and CO 2 may cause marked disturbances both of the respiratory move- 

 ments and of the gaseous interchange. 



When the percentage of O in the inspired air is increased up to 40 volumes 

 per cent., Bert found that there occurred an increase in the quantity absorbed, 

 and both Speck and Fredericq have noted merely a transient increase under 

 similar circumstances ; but the results of most experimenters, on the contrary, 

 seem to show quite conclusively that an increase of the per cent, of O above 

 the normal does not affect the quantity absorbed. Lukjanow 1 in a large 

 number of experiments could not detect any increase, and Saint-Martin, 2 in 

 researches on guinea-pigs and rats with an atmosphere containing from 20 to 

 75 volumes per cent, of O, noted the same result. Even in an atmosphere of 

 pure O animals breathe as though they were respiring normal atmospheric air. 



A decrease in the percentage of O is without influence until the proportion 

 falls below 13 volumes per cent. Worm-Miiller long ago showed that animals 

 breathe quietly in air containing 14.8 volumes per cent, of O, and that if the 

 proportion fell to 7 volumes per cent., respiration became slow, deep, and diffi- 

 cult ; with 4.5 volumes per cent, marked dyspnoea occurred ; and when there 

 was but 3 volumes per cent, asphyxia rapidly supervened. The more recent 

 results of Speck 3 not only confirm the main facts of Worm-Muller's observa- 

 tions, but furnish other important data. He has shown that when the 

 atmosphere contains 13 volumes per cent, of O, respiration is quiet and the 

 quantity of O absorbed is but slightly, if at all, diminished, and that even 

 when the proportion falls to 9.65 volumes per cent, breathing is carried on for 

 a long time without inconvenience, the amount of O absorbed, however, being 

 diminished. He shows, moreover, that when the volume of O in the atmo- 

 sphere falls to 8 per cent, the respiratory movements are deep and are but 

 slightly accelerated, the quantity of O absorbed being very much diminished, 

 and that the animal subjected to such an atmosphere succumbs in a few 

 moments. The quantity of O taken into the lungs falls proportionately with 

 the diminution of O in the inspired air until the reduction reaches 11.26 vol- 

 umes per cent., but further diminution is compensated for by an increase in 

 the volume of air respired. As the volume per cent, of O in the inspired air 



1 Zeitschrift f. Physiolog. Chemie, 1883-1884, vol. 8, pp. 313-355. 



8 Compt. rend., 1885, vol. 98, pp. 241-243. 



3 Zeitschrift f. klin. Med., 1887, vol. 12, pp. 447-532. 



