146 ANIMAL PHYSIOLOGY. 



takes place. The face becomes livid with unaerated blood, 

 the veins of the neck swollen, the circulation in the lungs 

 stopped, and the heart gorged with dark blood, especially 

 on the right side : there is evidence that the systemic as 

 well as the pulmonary capillaries refuse to allow the blood to 

 pass through them (Dalton), and death quickly supervenes, 



Even a slight interference with respiration retards the 

 circulation, and this interference may be caused by impeded 

 expiration, as in blowing a trumpet, or violent spasmodic 

 expiration, as in coughing, in both which cases the veins of 

 the neck are seen to swell ; or, by impeded inspiration, as in 

 asthma, or by inhalation of a poisoned atmosphere, in which 

 cases the hindrance to circulation is the vitiated condition of 

 the blood. 



The cessation of circulation, however, is not the cause of 

 death by asphyxia; that is rather to be imputed to the 

 poisonous influence of vitiated blood on the brain. Arrest 

 of the heart's action, constituting the condition known as 

 syncope or fainting, may be recovered from after a period of 

 time to which it is difficult to name a limit ; but asphyxia 

 causes death in less than five minutes, and even more 

 speedily in drowning, which is complicated by entrance of 

 water into the lungs. The few recorded instances of recovery 

 after submergence for longer periods are to be accounted for 

 by supposing that the patient fainted at the moment of falling 

 into the water, or before falling in, and so had lain without 

 effort at inspiration. 



110. It is of importance to observe that air may be 

 vitiated by many impurities besides carbonic acid. Prin- 

 cipal among these are minute particles of living and 

 dead organic matters floating in the air, and products of 

 decomposition of organic debris. The precise nature and 

 properties of the different substances with which the air may 

 be filled are difficult to determine. It must not be supposed 

 that things which are offensive to the senses are necessarily 

 deleterious to the health. There is no proved relationship 

 between the intensity of bad smells and insalubrity of the air, 

 and many invectives about poisoned atmospheres, sufficiently 

 excellent in their general tendency, are based on very slender 

 scientific foundation. But while it is admitted that un- 



