78 
ENOS WALTER. 
the nerves of general sensibility. In either case this center 
reflects motor impulses to the respiratory muscles through 
the phrenic, intercostals, inferior laryngeal and other nerves.” 
[Brubaker]. 
“ The respiratory center, while not dependent upon 
impulses coming through afferent nerves, is especially modi¬ 
fied in activity by impulses traveling through the pneumo- 
gastric nerves. If one pneumogastric nerve be cut, respira¬ 
tion becomes slower and deeper, while the pauses between the 
respiratory movements are more prolonged. If both be cut, 
the same is true to a greater extent, and the amount of oxygen 
absorbed and carbon di-oxide exhaled remains the same. Irri¬ 
tation of the central ends of the cut pneumogastrics inci eases 
the rapidity of respiration. The vagus may then be consid¬ 
ered as a stimulating nerve to the respiratory center, and the 
laryngeal nerves as inhibitory nerves to that center, which 
when stimulated arrest respiration, the diaphragm being in a 
state of relaxation and the thorax contracted. 
“ Deficient oxygenation of the blood acts as a stimulant to 
the respiratory center and causes the respiratory movements 
to become quicker as well as deeper, while expiration becomes 
especially increased in power. In a greater degree the depri¬ 
vation of oxygen from the blood appears to cause the exten¬ 
sion of the stimulus from the respiratory center to other 
adjoining motor centers and we find not only.are the ordinary 
muscles of respiration thrown into violent action, but that 
every muscle in the body connected with respiration is 
thrown into a state of forced contraction. Such a state is 
described as dyspnoea. 
“ Ligating the vertebral and carotid arteries produces dys¬ 
pnoea by decreasing the supply of oxygenated blood brought 
to this center. So weak heart may cause it, and so also may 
temperature above the normal, from the fact that increased 
temperature leads to increased activity of chemical processes 
and so to rapid exhaustion of oxygen. 
“ From deprivation of oxygen the first stage is dyspnoea,' 
characterized by extraordinary efforts of the muscles of respi-: 
ation, expiration being especially convulsive.” [Smith]. 
