RESPIRATION OF FOREIGN GASES. 271 



the carotid manometer rapidly falls. The left ventricle, now relieved 

 from the great internal pressure, may execute a few feeble beats, but 

 they can only be feeble, as its tissues have been subjected to the action 

 of the very impure blood. More and more blood accumulates in the 

 right side from the causes already mentioned. 



The violent inspiratory efforts in the early stages aspirate blood 

 from the veins towards the right side of the heart, but of course this 

 factor is absent when the chest is opened.] 



[Recovery from the condition of asphyxia. If the trachea of a dog be 



closed suddenly and completely, the average duration of the respiratory move- 

 ments is 4 minutes 5 seconds, while the heart continues to beat for about 7 minutes. 

 Recovery may be obtained if proper means be adopted before the heart ceases to 

 beat; but after this, never. 



If a dog be drowned, the result is different. After complete submersion for 14 

 minutes, recovery did not take place. In the case of drowning, air passes out of 

 the chest, and water is inspired into and fills the air-vesicles. It is rare for 

 recovery to take place in a person deprived of air for more than five minutes. If 

 the statements of sponge-divers are to be trusted, a person may become accustomed 

 to the deprival of air for a longer time than usual. In cases where recovery takes 

 place after a much longer period of submersion, it has been suggested that, in these 

 cases, syncope occurs, the heart beats but feebly or not at all, so that the 

 oxygen in the blood is not used up with the same rapidity. It is a well-known 

 fact that newly-born and young puppies can be submerged for a long time before 

 they are suffocated.] 



Artificial Respiration. The methods of performing artificial respira- 

 tion in persons apparently suffocated are fully given in vol. ii., under 

 Nervous Mechanism of Respiration. 



135. Respiration of Foreign Gases. 



No gas without a sufficient admixture of O can support life. Even with com- 

 pletely innocuous and indifferent gases, if no O be mixed with them, they cause 

 suffocation in 2 to 3 minutes. 



I. Completely indifferent gases are N, H, CELi. The living blood of an 

 animal breathing these gases yields no O to them (Pfluger). 



II. Poisonous gases- () Those that displace O, and form a permanent 

 stable compound with the hsemoglobin (1.) CO ( 16 and 17). (2.) CNH 

 (Hydrocyanic acid) displaces (?) O from haemoglobin, with which it forms a 

 more stable compound and kills exceedingly rapidly. It prevents O being changed 

 into ozone in the blood. Blood-corpuscles charged with hydrocyanic acid lose the 

 property of decomposing hydric peroxide into water and O ( 17, 5). 



(b.) Narcotic gases. (1.) C0 2 v. Pettenkofer characterises air containing O 

 with '1 p.c. C0 2 as "bad air ; " still, air in a room containing this amount of C0 2 

 produces a disagreeable feeling rather from the impurities mixed with it than from 

 the actual amount of COa itself. Air containing 1 p.c. C0 2 produces decided 

 discomfort, and with 10 p.c. it endangers life, while larger amounts cause death 

 with symptoms of coma. (2.) N 2 (nitrous oxide) respired, mixed with volume 

 O, causes, after 1 to 2 minutes, a short temporary stage of excitement ("Laughing 

 gas" of H. Davy), which is succeeded by unconsciousness, and afterwards an 

 increased excretion of C0 2 - (3.) Ozonised air causes similar effects (Binz). 



