INTEODUCTION. 9 



Respirations consist of two acts^ inspiration and 

 expiration. The former is brought about by elevation of 

 the ribsj and contraction of the diaphragm — both acts of 

 muscular exertion. The effect of contraction of the 

 diaphragm is to lessen its concavity towards the abdomen, 

 hence it presses on the abdominal viscera and causes 

 bulging of the walls of the belly. Expiration under 

 ordinary circumstances depends upon elastic recoil of the 

 elevated walls of the thorax_, resulting in expulsion of air 

 through the trachea and larynx. Respirations vary with 

 their depth, frequency, quickness, facility, and the nature 

 of the movements by which they are brought about. Thus, 

 they may be quick or slow, frequent or infrequent, deep 

 or imperfect, laboured, unequal, irregular, &c. 



Dyspn(ea is a term used to imply difficulty of breathing 

 of any kind. 



Apn(EA is the extreme of infrequent respiratory effort, 

 dependent upon the circulation of highly oxygenated 

 blood through the medulla oblongata, where the respira- 

 tory centre resides. Until its natural stimulus, venous 

 blood, is supplied to this centre, no respiratory effort will 

 occur. 



Oethopncea is that condition in which difficulty of 

 respiration is marked except when the animal is in a 

 standing position. 



Asphyxia (literally pulselessness) is a complicated con- 

 dition due to insufficient supply of air for respiratory 

 purposes. It commences as dyspnoea, convulsions with 

 violent expiratory efforts succeed, and, finally, exhaustion 

 sets in, leading to death. In the later stages of asphyxia 

 the animal is stretched out in a recumbent position, with 

 dilated pupils, loss of general sensibility, scarcely per- 

 ceptible pulse, visible mucous membranes dark purple in 

 colour, respirations deep and slow. Finally, he gasps 

 for breath, extends the limbs, shudders, and dies. And 

 on post-mortem examination the lungs, right side of 

 the heart, medulla oblongata, and various body tissues 

 are found in a state of venous engorgement. Lungs, 

 heart, and medulla are all concerned in the fatal result. 



