322 VETERINARY PHYSIOLOGY 



the long winter sleep of certain animals (hibernation), these 

 factors, as well as the diminished temperature of the body, 

 cause a great reduction in the intake of oxygen and output 

 of carbon dioxide. 



It is thus the internal, which governs external respiration. 

 Merely increasing the number or depth of the respirations has 

 only a transient influence on the amount of the respiratory 

 interchanges. 



Asphyxia 



This is the condition caused by any interference with the 

 supply of oxygen to the blood and tissues. It may be induced 

 rapidly and in an acute form by preventing the entrance of 

 air to the lungs, as in drowning or suffocation, or by causing 

 the animal to breathe air deprived of oxygen, or by interfer- 

 ing with the flow of blood through the lungs, or with the 

 oxygen-carrying capacity of the blood. It is slowly induced 

 in a less acute form when the muscles of respiration fail as 

 death approaches. 



In acute asphyxia there is an initial stage of increased 

 respiratory effort, the breathing becoming panting, and the 

 expirations more and more forced. The pupils are small, and 

 the heart beats more slowly and more forcibly, while the 

 urterioles are strongly contracted, and a marked rise in the 

 arterial pressure is produced. When the vagi are cut the 

 slowing of the heart does not occur. Within a couple of 

 minutes a general convulsion, involving chiefly the muscles 

 of expiration, occurs. The intestinal muscles and the muscles 

 of the bladder may be stimulated, and the fseces and urine 

 may be passed involuntarily. Then the respirations stop, deep 

 gasping inspirations occurring at longer and longer intervals. 

 The pupils are dilated, and consciousness is abolished. The 

 heart fails, and thus, although the arterioles are s-till contracted, 

 the pressure in the arteries falls. Finally the movements 

 of the heart cease and death supervenes. 



