SENSE. OF SUFFOCATION. 167 



every five to eight respirations, or when the respiratory movements are a little restricted 

 under the influence of depressing emotions, an involuntary deep or sighing inspiration is 

 made, for the purpose of changing the air in the lungs more completely. The increased 

 consumption of oxygen and a certain amount of interference with the mechanical process 

 of respiration during violent muscular exercise put us " out of breath," and for a time 

 the respiratory movements are exaggerated. This is perhaps the first physiological way 

 in which the want of air is appreciated by the senses. A deficiency in hsematosis, either 

 from a vitiated atmosphere, mechanical obstruction in the air-passages, or grave trouble 

 in the general circulation, produces all grades of sensations, from the slight oppression 

 which is felt in a crowded room, to the intense distress of suffocation. When haamatosis 

 is but slightly interfered with, only an indefinite sense of oppression is experienced, and the 

 respiratory movements are a little increased, the most marked effect being an increase in 

 the number and extent of sighing inspirations. In the experiments upon animals to which 

 we have referred, when artificial respiration was interrupted, we first noticed regular and 

 not violent contractions of the respiratory muscles ; but, as the sense of want of air be- 

 came exaggerated, every muscle which could be used to raise the chest was brought into 

 action. In the human subject in this condition, the countenance has a peculiar expres- 

 sion of anxiety and distress, and the movements soon extend to the entire muscular sys- 

 tem, resulting in general convulsions, and, finally, in insensibility. 



Bearing in mind the fact that, although these sensations are referred to the lungs, 

 indicating increased respiratory effort as the common means for their relief, they have 

 their real point of departure in the general system, we can understand the operation of 

 various abnormal conditions of the circulation, when the lungs are adequately supplied 

 with fresh air. The first subjective symptom of air in the veins is a sense of impending 

 suffocation. There is no want of air hi the lungs, but the circulation is instantaneously 

 interrupted, and oxygenated blood is not supplied to the tissues. The same effect, practi- 

 cally, follows abstraction of the circulating fluid or the absorption of any poisonous agent 

 which destroys the function of the corpuscles as carriers of oxygen; although, in haemor- 

 rhage, the effects are not so marked, as generally the system is gradually debilitated by 

 the progressive loss of blood. It was invariably noticed, in the experiments above referred 

 to, that, after the division of a large artery, although artificial respiration was carefully 

 performed, respiratory efforts took place when the system became nearly drained of blood. 

 As the hasmorrhage continued, these efforts became more violent and resulted, just before 

 death, in general convulsions. A comparison of this experiment with those in which 

 artificial respiration was simply interrupted shows that, in sudden haemorrhage, there can 

 be no doubt that the system feels the want of oxygen ; and, when the loss of blood is 

 very great, this is increased until it amounts to a sense of suffocation. In gradual haemor- 

 rhage, there is a conservative provision of Nature, by which faintness and diminution in 

 the force of the heart's action favor the arrest of the flow of blood. 



Poisoning by carbonic oxide is generally accompanied with convulsions, which arise 

 from the sense of suffocation and are due to a fixation of this gas in the blood-corpuscles, 

 by which they are rendered incapable of carrying oxygen to the system. Convulsions also 

 attend poisoning by hydrocyanic acid, in cases in which the system is not overpowered 

 immediately by a large dose of this agent and the muscular irritability is destroyed. 



Experiments have failed to show that the respiratory sense, or the sense of suffocation, 

 is due to irritation produced by carbonic acid in the non-oxygenated blood. 



Respiratory Efforts before Birth. 



It is generally admitted that one of the most important functions of the placenta> and 

 the one which is most immediately connected with the life of the foetus, is a respiratory 

 interchange of gases, analogous to that which takes place in the gills of aquatic animals. 

 The vascular prolongations from the foetus are continually bathed in the blood of the 

 mother, and this is the only way in which it can receive oxygen. Notwithstanding the 



