408 ANIMAL PHYSIOLOGY. 
SPECIAL CONSIDERATIONS. 
Pathological and Clinical—_ The number of diseases that lessen 
the amount of available pulmonary tissue, or hamper the move- 
ments of the chest, are many, and only the briefest reference 
can be made to a few of them. 
Inflammation of the lungs may render a greater or less por- 
tion of one or both lungs solid; inflammation of the pleura 
(pleuritis, pleurisy) by the dryness, pain, etc., may restrict the 
thoracic movements; phthisis may solidify or excavate the lungs, 
or by pleuritic inflammation glue the costal and pulmonary 
pleural surfaces together; bronchitis clog the tubes and other 
air-passages with altered secretions; emphysema (distention of 
air-cells) may destroy elasticity of parts of the lung; pnewma- 
thorax from rupture of the lung-tissue and consequent accumu- 
lation of gases in the pleural cavity, or pleurisy with effusion, 
render one lung all but useless from pressure. In all such 
cases Nature attempts to make up what is lost in amplitude by 
increase in rapidity of the respiratory movements. It is inter- 
esting to note too how the other lung, in diseased conditions, if 
-it remain unaffected, enlarges to compensate for the loss on the 
opposite side. When the muscles are weak, especially if there 
be hindrance to the entrance of air while the thoracic move- 
ments are marked, there may be bulging inward of the inter- 
* costal spaces. 
Normally, this would also occur, as the intra-thoracic press- 
ure is less than the atmospheric, were it not for the fact that 
the intercostal muscles when contracting have a certain resist- 
ing power. 
The imperfect respiration of the moribund, permitting the 
accumulation of carbonic anhydride with its soporific effects, 
smooths the descent into the valley of the shadow of death; so 
that there may be to the uninitiated the appearance of a suffer- 
ing which does not exist, consciousness itself being either 
wholly or partially absent. The dyspnoea of anemic persons, 
whether from sudden loss of blood or from imperfect renewal 
of the hemoglobin, shows that this substance has a respiratory 
function; while in forms of cardiac disease with regurgitation, 
etc., the blood may be imperfectly oxidized, giving rise to la- 
bored respiration. 
Personal Observation—As hinted from time to time during 
the treatment of this subject, there is a large number of facts 
the student may verify for himself. 
