244 RESPIRATION IN A CLOSED SPACE. 



RESPIRATION IN A CLOSED SPACE, OR WITH ARTIFICIAL 



CHANGES IN THE AMOUNTS OF OXYGEN AND CARBON 



DIOXID IN THE RESPIRED AIR. 



Respiration in a closed space results in (i) a gradual diminution of the oxygen, 

 (2) a simultaneous increase of the carbon dioxid, and (3) a diminution in the 

 volume of gas. If the space is only of moderate size, the animal consumes the 

 oxygen almost completely, the blood becomes almost free of oxygen, and death 

 finally results, accompanied by asphyxial convulsions. The absorption of oxygen 

 occurs, therefore, through chemical combination, independently of the laws of 

 absorption. 



In larger closed spaces considerable accumulation of carbon dioxid takes 

 place before the oxygen is diminished to such an extent that life is threatened. 

 As the carbon dioxid can be excreted from the body only when its tension is greater 

 in the blood than in the surrounding air, there will be retention of the gas as the 

 amount expired into the enclosed space increases; and, finally, a return of the 

 carbon dioxid into the body may take place. This occurs while the oxygen is 

 still sufficient to support life. Death results, therefore, directly from poisoning by 

 carbon dioxid, with the symptoms of dyspnea of short duration, to which are 

 added stupor and subnormal temperature. This manner of death has been ob- 

 served in rabbits, after they had reabsorbed some of the carbon dioxid that had 

 been excreted previously by them. 



In pure oxygen, or in an atmosphere rich in oxygen, animals breathe in a per- 

 fectly normal manner. A little more oxygen is absorbed, but still the amount of 

 carbon dioxid excreted is not increased. In closed spaces filled with oxygen, 

 animals finally die through the reabsorption of their excreted carbon dioxid. 

 Rabbits have thus been observed to die after they had absorbed an amount of 

 carbon dioxid equal to half the volume of their body, although the enclosed air 

 still contained over 50 per cent, of oxygen. 



Human beings and animals can still breathe an air-mixture containing only 

 9 per cent, of oxygen; deepened respirations set in at 10 per cent., and discomfort 

 at 8 per cent. Animals breathe with difficulty and lose consciousness at 7 per 

 cent.; pronounced dyspnea makes its appearance at 4.5 per cent., and quite 

 rapid suffocation at 3 per cent. The air expired by man under normal conditions 

 still contains between 14 and 18 per cent, of oxygen. Mammals placed in a gaseous 

 mixture poor in oxygen consume slightly less oxygen. 



The metabolism of animals is unchanged by variations in the amount of 

 oxygen in the respired air between the limits of 10.5 and 87 per cent. If the 

 oxygen falls below 10.5 per cent., there is an increase in the excretion of nitrogen, 

 carbon dioxid, lactic acid, and oxalic acid through the urine. 



If the amount of carbon dioxid in the inspired air be increased, the respiratory 

 movements are increased, but the excretion of carbon dioxid and the absorption of 

 oxygen are diminished. 



Inspiration is actively stimulated by a deficiency of oxygen, as well as by an 

 excess of carbon dioxid. The dyspnea that is induced under the condition first 

 stated is prolonged and severe, while under the second condition the respiratory 

 activity soon diminishes. A deficiency of oxygen further causes a greater and 

 more prolonged rise in the blood-pressure than does an excess of carbon dioxid. 

 Finally, the consumption of oxygen by the body is less restricted by a diminution 

 of the oxygen in the air than by an excess of carbon dioxid. Death from limitation 

 in the supply of oxygen is preceded by violent irritative phenomena and convul- 

 sions, which are absent in case of death from excess of carbon dioxid. Finally, in 

 conjunction with poisoning by carbon dioxid, the excretion of this gas is greatly 

 diminished. 



If animals be supplied with a gaseous mixture similar to the atmosphere, but 

 in which the nitrogen is replaced by hydrogen, they breathe quite normally; the 

 hydrogen of the mixture does not undergo any noteworthy change in volume. 

 Increase or diminution in the amount of nitrogen in the air simply causes a greater 

 or lesser absorption of the gas by the fluids of the body. 



Cl. Bernard found that if an animal be made to respire in a closed space, 

 it became, up to a certain point, accustomed to the successive deterioration of 

 the air. If he placed a bird under a glass bell-jar, it lived for several hours; but 

 if, before its death, another bird were added from the fresh air, the latter imme- 

 diately died in convulsions. 



