548 VETERINARY PHYSIOLOGY 



E. VENTILATION. 



The rate of gaseous exchange governs the necessary supply 

 of fresh air. The subject is considered under Stable Manage- 

 ment. In byres, some 800 cubic feet are generally allowed per 

 cow. 



The bad effects of breathing in a crowded, close, badly- 

 ventilated space is dealt with on p. 538. 



F. ASPHYXIA. 



This is the condition caused by any interference with the 

 supply of oxygen to the blood and to the tissues, (a) It may be 

 induced rapidly and in an acute form by preventing the entrance 

 of air to the lungs, as in drowning or suflfocation, or by causing 

 the animal to breathe air deprived of oxygen, or by interfering 

 with the flow of blood through the lungs, or with the oxygen- 

 carrying capacity of the blood, as in CO poisoning, or with the 

 processes of oxidation in the tissues, as in poisoning with 

 cyanides, (b) It is slowly induced, in a less acute form, when 

 the muscles of respiration fail as death approaches. 



In acute asphyxia there is (1) an initial stage of increased 

 respiratory effort due to the accumulation of C0„, the breath- 

 ing becoming panting, and the expirations more and more 

 forced. The pupils are contracted, and the heart beats more 

 slowly and more forcibly, while the arterioles are strongly 

 contracted, and a rise in the arterial pressure is generally 

 produced. In some animals this is very transitory. When 

 the vagi are cut, the slowing of the heart does not occur, 

 and the rise of blood pressure may be more marked. (2) 

 Usually 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 fa3ces and urine may be passed involuntarily. 

 (3) Then, as the result of oxygen want, 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 



