RESPIRATION. 425 



in the pressure of the CO 2 and in how far to a stimulation of the vagus. 

 But inasmuch as apnea can be established, though not of such long duration, 

 after division of the vagus nerves, the probabilities are that the diminished 

 percentage of the CO 2 is the main cause. 



Dyspnea. Excessive and laborious respiratory movements constitute 

 a condition known as dyspnea. Movements of this character indicate that 

 the blood contains a greater percentage of CO 2 than normal or a diminished 

 percentage of oxygen. In either case the excitability of the inspiratory center 

 is abnormally heightened. Of the two conditions, the former is by far the 

 more common. While it is true that a deficiency of oxygen in the arterial 

 blood gives rise to an increase in the rate and depth of the inspiratory move- 

 ments, this does not arise until the deficiency of the oxygen falls to about 

 one-third of the normal. On the other hand, an increase of even 0.2 per 

 cent, of CO 2 in the alveolar air will almost double the respiratory activity. 



A deficiency in the amount or the quality of the hemoglobin is usually 

 attended with more or less dyspnea. These conditions of the blood may be 

 caused: (i) By all those pathologic conditions of the respiratory apparatus 

 which limit the free entrance of oxygen into and the free exit of carbon 

 dioxid from the blood; (2) by those alterations in the composition of the air 

 and subsequently in the blood which arise when the individual is confined in a 

 space of moderate size with imperfect ventilation. 



Asphyxia. If the state of the blood observed in dyspnea be exaggerated 

 that is, if the increase in the percentage of carbon dioxid become more 

 marked the respiratory movements become more laborious. A con- 

 tinuance of this changed composition of the blood eventuates in death. 

 Before this occurs the individual exhibits a succession of phenomena, to the 

 totality of which the term asphyxia is given. 



Asphyxia may be caused : (i) By a sudden interference with the entrance 

 of oxygen into and the exit of carbon dioxid from the blood, as in drowning, 

 occlusion of the trachea from any cause, double pneumothorax, etc. (2) 

 By confinement in a small space the air of which speedily undergoes a loss 

 of oxygen and an accumulation of carbon dioxid. In the first instance 

 death may occur in a few minutes; in the second instance it may be postponed 

 several hours or more, the time varying with the size of the space. 



The succession of phenomena presented by an individual in the asphyxi- 

 ated condition is as follows: Increased rate and depth of the respiratory 

 movements, passing rapidly from hyperpnea to dyspnea, with an active con- 

 traction of all the muscles concerned in respiration, ordinary and extraor- 

 dinary ; a blue, cyanosed condition of the face from the rapid accumulation 

 of carbon dioxid and disappearance of the oxygen of the blood; a diminution 

 in the depth of inspiration and an increase in the force and extent of ex- 

 piration, followed by general convulsions; collapse, characterized by un- 

 consciousness, loss of the reflexes, relaxation of the muscles, a weak action of 

 the heart, a disappearance of the pulse, and death. As shown by observation 

 of the circulatory apparatus in artificially induced asphyxia, there is primarily 

 an increase in the activity of the heart, soon followed by retardation; a rise 

 of blood-pressure in the early stages and a fall to zero after collapse has set 

 in. The retardation and final cessation of the heart, as well as the rise of 

 the blood-pressure, are to be attributed to stimulation of the cardio-inhibi- 



