3 o6 HUMAN PHYSIOLOGY 



of the body cause a great reduction in the intake of oxygen 

 and output of carbon dioxide. 



It is thus the internal which governs the external respira- 

 tion. Merely increasing the number or depth of the 

 respirations has no influence on the amount of the 

 respiratory interchanges. 



Ventilation. 



The rate of gaseous exchange governs the necessary 

 supply of fresh air. It has been found that if the supply 

 is insufficient, headache and sleepiness are apt to supervene, 

 and experience has taught that each adult should have 

 2000 cubic feet of fresh air per hour. If 1000 cubic feet 

 of space is allowed to each individual, the ordinary methods 

 of exchange of air through the chimneys and through 

 chinks in windows and doors should supply this quantity 

 of air. 



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 interfering 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 as the muscles of respiration 

 fail as death from almost any disease 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 arterioles are strongly contracted, and a marked rise 

 in the arterial pressure is produced. 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 faeces 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 



