THE PULMONARY PLEXUS. 
181 
air, and you can suspend the expiration during double or treble 
the time that you could after ordinary breathing. It takes a 
longer time for the contained air to be so charged with carbon 
as to compel the expiration ot it. 
Incisions were made through the pleura of a dog, and a cur- 
rent of atmospheric air was driven down the trachea, and through 
the lungs. There was a constant supply of air for the arte- 
rialization of the blood. The breathing was suspended, but the 
dog lived. The artificial supply was then cut off, and from the 
injury done to the lungs, the breathing became convulsive to the 
highest degree. 
Braschet took a puppy of a few days old, and excised a portion 
of the spinal organic nerve on each side. He plunged the muzzle 
of the dog into water. The supply of pure air was cut off, and 
the dog presently died ; but, the spinal organic nerve being di- 
vided, there was nothing to convey to the medulla oblongata or to 
the brain the impression on the bronchial membrane, and there 
was not a struggle that could have reference to the respiratory 
apparatus. He plunged the muzzle of another puppy into the 
water without the division of these nerves, and he also died, but 
it was after long-continued convulsions. 
The Function of the Nerves o f the Pulmonary Plexus . — The 
office of these branches of the spinal organic nerves is evidently 
to cause the vesicles and the bronchial tubes to contract upon 
the contained air, and to expel a portion of that which had 
been vitiated by the abstraction of the oxygen, and the accumu- 
lation of carbonic acid. Without such an apparatus, this pur- 
pose could not have been accomplished. There are auxiliary 
agents of which I shall immediately speak, but which alone 
would not have been competent to the task. If,” says Dr. 
Quain, “ the lungs were simply passive, and therefore incapable 
of contributing to the expulsion of the air, the subsidence of 
the thorax upon them would only press the air out of the parts 
near their surface, but could exert little influence over those 
that are deeply seated.” 
The Auxiliary Muscles . — But there are other muscles con- 
cerned in the act of expiration, far more powerful than those of 
which I have been speaking ; such are the obliqui, the trans- 
versus, and the rectus abdominis, the quadratus lumborum, the 
serratus posticus inferior, and some others. 
The act of expiration having been performed, the bronchi and 
the vesicles having to a certain degree collapsed upon their con- 
tents, they once more expand, partly by their inherent elasticity, 
more by a vital power which they possess, and which is to be traced 
in every vessel, and every part intimately connected with life, but 
