398 ANIMAL PHYSIOLOGY. 
apnea, may be induced by pumping air into an animal’s chest 
very rapidly by a bellows; or in one’s self by a succession of 
rapid, deep respirations. 
After ceasing, the breathing may be entirely interrupted 
for a brief interval, then commence very quietly, gradually in- 
creasing to the normal. 
Apnea has been interpreted in two ways. Some think that 
it is due to fatigue of the muscles of respiration or the respira- 
tory center; others that the blood has under these circum- 
stances an excess of oxygen, which so influences the respiratory 
center that it is quieted (inhibited) for a time. 
The latter view is that usually adopted ; but, considering that 
apnea results from the sobbing of children following a pro- 
longed fit of crying, also in Cheyne-Stokes and other abnormal 
forms of breathing, and that the blood is normally almost satu- 
rated with oxygen, it will be agreed that there is a good deal 
to be said for the first view, especially that part of it which 
represents the cessation of breathing as owing to excessive 
activity and exhaustion of the respiratory center. We find 
such a calm in asphyxia after the convulsive storm. 
Is it, then, the excessive accumulation of carbon dioxide or 
the deficiency of oxygen that induces dyspnea? Considering 
that the former gas acts as a narcotic, and does not induce con- 
vulsions, even when it constitutes a large percentage of the 
atmosphere breathed, and that the need of oxygen for the tis- 
sues is constant, it certainly seems most reasonable to conclude 
that the phenomena of dyspnea are owing to the lack of oxy- 
gen chiefly, at least; though the presence of an excess of car- 
bonic anhydride may take some share in arousing that vigorous 
effort on the part of the nervous system, to restore the func- 
tional equilibrium, so evident under the circumstances. 
The Cheyne-Stokes Respiration (Phenomenon).—There is a form 
of breathing occurring under a variety of abnormal circum- 
stances, in which the respirations gradually reach a maximum 
(dyspnea), and then as gradually decline to absolute cessation 
(apnoea). The pause may last a surprising length of time (one 
half to three quarters of a minute), when this form of breathing 
again repeats itself. It has been compared to the periodic 
grouping of heart-beats (Luciani groups), occurring when the 
organ is suffering. There is abundant cause usually for ex- 
haustion of the center, on account of disordered blood or an 
insufficient supply to the brain. This phenomenon and apnea 
bring out clearly the rhythmic character of those processes, 
