96 



RESPIRATION IN A LIMITED SPACE. 



the urine, but when they are administered as alkaline compounds they are changed into 

 carbonates. .... 



133. RESPIRATION IN A LIMITED SPACE. Respiration in a limited 

 tpace causes (1) a gradual diminution of O ; (2) a simultaneous increase of C0 2 ; 

 (3) a diminution in the volume of the gases. If the space be of moderate dimen- 

 sions, the animal uses up almost all the O contained therein, and dies ultimately 

 from spasms caused by the asphyxia. The O is absorbed, therefore independently 

 of the laws of absorption by chemical means. The O in the blood is almost com- 

 pletely used up ( 129). In a larger space, the C0 2 accumulates rapidly, before 

 the diminution of O is such as to affect the life of the animal. As C0 2 can only 

 be excreted from the blood when the tension of the C0 2 in the blood is greater 

 than the tension of C0 2 in the air, as soon as the C0 2 in the surrounding air in 

 the closed space becomes the same as in the blood, the C0 2 will be retained in the 

 blood, and finally C0 2 may pass back into the body. This occurs in a large closed 

 space, when the amount of O is still sufficient to support life, so that death occurs 

 under these circumstances (in rabbits) through poisoning with C0 2 causing 

 diminished excitability, loss of consciousness, and lowering of temperature, but no 

 spasms ( Worm Mutter). In pure animals breathe in a normal way ; the quantity 

 of O absorbed and the C0 2 excreted is quite independent of the percentage of O, 

 so that the former occurs through chemical agency independent of pressure. In 

 limited spaces filled with O, animals died by absorption of the C0 2 excreted. 

 Worm Miiller found that rabbits died after absorbing C0 2 equal to half the volume 

 of their body, although the air still contained 50 per cent. 0. Animals can 

 breathe quite quietly a mixture of air containing 14 '8 per cent. (20*9 per cent, 

 normal) ; with 7 per cent, they breathe with difficulty ; with 4 "5 per cent, there is 

 marked dyspnoea ; with 3 per cent. O there is tolerably rapid asphyxia. The air 

 expired by man normally contains 14 to 18 per cent. O. According to Hempner, 

 mammals placed in a mixture of gases poor in O use slightly less O. 



Dyspncea occurs when the respired air is deficient in 0, as well as when it is overcharged 

 with C0 2 , but the dyspnoea in the former case is prolonged and severe ; in the latter, the 

 respiratory activity soon ceases. The want of causes a greater and more prolonged increase 

 of the blood-pressure than is caused by excess of C0 2 . Lastly, the consumption of in the 

 body is less affected when the in the air is diminished than when there is excess of C0 2 . If 

 air containing a diminished amount of be respired, death is preceded by violent phenomena 

 of excitement and spasms, which are absent in cases of death caused by breathing air over- 

 charged with C0 2 . In poisoning with C0 2 , the excretion of C0 2 is greatly diminished, while 

 with diminution of O it is almost unchanged. 



If animals be supplied with a mixture of gases similar to the atmosphere, in 

 which N is replaced by H, they breathe quite normally (Lavoisier and Seguin) ; 

 the H undergoes no great change. 



CI. Bernard found that, when an animal breathed in a limited space, it became partially 

 accustomed to the condition. On placing a bird under a bell-jar, it lived several hours ; but 

 if several hours before its deatbj another bird fresh from the outer air were placed under the 

 same bell-jar, the second bird died at once, with convulsions. 



Frogs, when placed for several hours in air devoid of 0, give off just as much C0 2 as in air 

 containing 0, and they do this without any obvious disturbance. Hence, it appears that the 

 formation of C0 2 is independent of the absorption of 0, and the C0 2 must be formed from the 

 decomposition of other compounds. Ultimately, however, complete motor paralysis occurs, 

 whilst the circulation remains undisturbed (Aubert). 



[134. DYSPNOEA AND ASPHYXIA. For the causes of dyspncea see 111, 

 and those of asphyxia see 368. If from any cause an animal be not supplied with 

 a due amount of air, normal respiration becomes greatly altered, passing through the 

 phases of hyperpnoea, or increased respiration, dyspnoea, or difficulty of breathing, 

 to the final condition of suffocation or asphyxia. The phenomena of asphyxia 

 may be developed by closing the trachea of an animal with a clamp, or by any 

 means which prevents the entrance of air or blood into the lungs. 



