268 DYSPNCEA AND ASPHYXIA, 



they breathe with difficulty; with 4'5 per cent, there is marked dyspnoea ; 

 with 3 per cent. there is tolerably rapid asphyxia (W. Miiller). The 

 air expired by man normally contains 14-18 per cent. 0. 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. 



Dyspnoea occurs when the respired air i.s 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 

 O 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 by breathing air over- 

 charged with C02. In poisoning with COo. the excretion of COo, is greatly 

 diminished, while with diminution of 0, it is almost unchanged (C. Friedlander 

 and E. Herter). 



Cl. Bernard found that, when an animal breathed in a closed 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 death 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 

 C02 as in air containing 0, and they do this without any obvious disturbance 

 (Pfliiger, Aubert). Hence, it appears that the formation of COo is independent of 

 the absorption of O, 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. 



[The causes of dyspnoea have already been referred to ( 111), and 

 those of asphyxia are referred to in detail in vol. ii. under Nervous 

 Mechanism of Respiration. 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 in an 

 animal by closing its trachea by means of a clamp, and in fact by any 

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



The phenomena of asphyxia are usually divided into several stages. 

 1. During the first stage there is hyperpnoea, the respirations being 

 deeper, more frequent, and laboured. The extraordinary muscles of 

 respiration both those of inspiration and expiration referred to in 

 118, are called into action, the condition of dyspnoea being rapidly 

 produced, and the struggle for air becomes more and more severe. 

 During this time the oxygen of the blood is being used up, the blood 



