THE MECHANISM OP RESPIRATION. 
GOT 
to be modified and changed. One of the ingredients in atmo¬ 
spheric air is oxygen, which has a strong affinity for the carbon, 
and also for these other matters, and a double decomposition or 
change of principles takes place in these little cells in which the 
blood and the air has been brought into contact. 
The carbon quits the blood and combines with some of the 
oxygen of the air, and forms carbonic acid ; and more of the 
oxygen quits the air and unites with these unknown substances 
in the blood for which it has affinity, and by this loss of carbon 
and gain of oxygen the blood is changed from venous to arterial— 
from inefficient to efficient—the contractility of the tissues to 
which it is sent is preserved, and all the functions of life are 
discharged. 
You see, then, with what important physiological matter this 
respiratory system is full; and that, with reference to pathology, 
it contains next to, or more than the foot, that which interests us 
in pathology. Nasal gleet, glanders, roaring, bronchitis, catarrhal 
fever, pneumonia, pleurisy, broken wind, thick wind, and various 
other chest affections, wili pass in review before us; and, indirectly, 
many a subject will be involved most intimately connected with 
the health and usefulness of all domesticated animals. 
The respiratory passages open on the external air at the nostrils 
of the horse, and at the mouth and nostrils of our other patients. 
The mechanism of the velum palati, or soft palate, prevents the 
horse from breathing through his mouth. The nasal cavity will 
therefore first come under consideration. 
Its bony structure is thus composed :—Superiorly and laterally 
w 7 e observe the nasal bones;—laterally and more inferiorly, the 
nasal surface of the superior maxillary bones,—and also laterally, 
but more anteriorly, the anterior maxillaries;—closing it posteri¬ 
orly, the eethmoid bones;—inferiorly, and constituting the floor, 
the palatine processes of the anterior maxillary, anteriorly ; the pa¬ 
latine processes of the superior maxillary, centrally; and the 
crescentic border of the palatine bones, posteriorly: and lying 
along the middle of the floor, and supporting in its groove the 
cartilaginous septum, is the vomer. The contents of the ca¬ 
vity on either side are, the convoluted portion of the sethmoid 
bones; the posterior and anterior turbinated bones; the lachrymal 
duct; and the bony canal, the canalis infra orbitarius, conduct¬ 
ing the facial portion of the anterior maxillary nerve, to be dis¬ 
tributed over the lips and lower part of the face. 
I will endeavour to give a brief description of each. First, 
observe the nasal bones in the horse, occupying the greater 
part of the face. We find them connected, externally, with the 
