CHAPTER III. 
THE CHEST AND ORGANS OF RESPIRATION. 
The thorax, or chest, is a large chamber bounded laterally by 
the ribs and their muscles, above by the spine, below by the breast- 
bone, and behind by an obliquely placed musculo-tendinous partition 
which separates it from the abdominal cavity, and known as the 
diaphragm or midriff. It contains the heart and respiratory organs 
and is deep and narrow. From researches conducted in recent 
years by M. Alfred Giard * and others it has been found that the 
pleural cavity, although present in the young elephant, is obliterated 
in the adult. This is a condition entirely different from what 
occurs in most mammals in which the lungs, though lying in contact 
with, have no actual attachment to the walls. This peculiarity is 
adapted to his mode of life, which seldom subjects him to respiratory 
emergencies, and his organization which does not necessitate rapid 
blood oxygenation. 
In the lungs the blood cells are furnished with oxygen, which 
being circulated by means of the heart distribute it to the tissues 
which build up the system. Oxygen is necessary to the life of those 
tissues. To effect this charging of the blood cells with oxygen 
breathing is constantly going on, and consists of two acts : the first 
during which air is conveyed through the respiratory passages to the 
lungs to purify the blood (inspiratory act), and the second during 
which air with impure products generated in the system is thrown 
out (expiratory act). During inspiration the chest expands and on 
expiration it contracts. In health this double act is performed on 
an average 12 to 16 times a minute. 
The respiratory organs, — The respiratory tract consists of — 
Nostrils. Wind-pipe. 
Nasal chambers in the skull. Lungs. 
Nose. — The nasal apparatus consists of certain structures which 
serve to form two passages, whose function is to conduct air from 
without into the air chambers in the bones of the skull, and also to 
* Comptes rendus des stances de I'Academie des Sciences, CXLIV, page 306, 
nth February 1907, by M. Alfred Giard. 
Comptes rendus des stances de I'Academie des Sciences, CXLIV, page 471, 
4th March 1907. 
Comptes rendus des stances de rAcad^mie des Sciences, CXLIV, page 318, 
€7th June 1907. 
