RESPIRATION 183 



heart's action grows rapidly weaker, although for two or three 

 minutes longer it may still continue to nicker. Recovery is 

 possible until it finally gives up. After death the right side of 

 the heart is found gorged with blood, the left side empty, 

 showing that the heart had been unable to force the blood 

 through the capillaries of the lungs. 



Under all ordinary conditions the sequence of phenomena 

 of asphyxia is the same a stage of exaggerated breathing 

 (hyperpncea), a stage marked by the co-operation of muscles 

 which are not called into action in tranquil breathing (dyspnoea), 

 followed by the condition of asphyxia properly so termed. 

 An animal whose supply of fresh air is cut off passes through 

 these three stages, whether it be enclosed in a small space or 

 in a very large one. It must, however, be noted that in 

 asphyxia several factors combine in varying degrees. Carbonic 

 acid is in excess in the blood, oxygen deficient. The nervous 

 mechanism which regulates respiratory movements is thrown 

 out of gear. Motor and inhibitory impulses are in conflict. 

 It is important, if these complex phenomena are to be analysed, 

 that one factor only should be altered at any given time. For 

 example, carbonic acid may be allowed to increase in the air 

 while a constant oxygen-tension is maintained. Under these 

 circumstances the dyspnoaic contractions are much less marked. 

 No convulsions follow. The paralysing action of carbonic acid 

 predominates. Anaesthesia passes into complete unconscious- 

 ness. Death is tranquil. And this, speaking generally, is 

 what happens in disease of the lungs. Asphyxia comes on 

 slowly. The supply of oxygen is undiminished, but carbonic 

 acid accumulates in the blood, acting as a narcotic poison which 

 lowers the excitability of the nervous system, suspends con- 

 sciousness, and slowly brings the vital activities to a standstill. 



In cases of drowning, when the lungs are filled with water, 

 the resistance to the passage of blood through their capillary 

 vessels is greater than it is when they are still filled with air. 

 The heart is sooner beaten in its effort to drive the blood 

 through them. Usually it stops in about four minutes. Yet 

 it is difficult to say for how long after a person has been im- 

 mersed in water it may be still possible to resuscitate him. 

 Reports vary, owing in large measure to uncertainty as to the 

 exact time at which the immersed person sank and his lungs 



