HYGIENE AND SANITATION 167 



tion in respiration means immediate oxygen starvation and 

 death. It is a continuous process, never ceasing a minute or 

 second till death of the bird. Such cessation and death by 

 shutting off the air-supply is called asphyxiation. 



The pressure of the carbon dioxid is lower in the systemic 

 capillaries than in the tissues, and the result is that there is a 

 constant diffusion through the capillary walls into the blood- 

 plasma, as the carbon dioxid is formed in the tissues through 

 combustion processes. The carbon dioxid thus passing into 

 the blood-plasma is carried to the lungs, where the venous 

 capillaries which are spread out, forming a network on the 

 surface of the lung tubules, allows it to diffuse through into 

 the air and is gotten rid of from the body. 



It is possible that the sodium carbonate of the blood unites 

 with the carbon dioxid in the blood-plasm, thus aiding in its 

 transportation. 



When birds are shut in a close coop or room, that is, one 

 without proper ventilation, so that there may be a proper 

 exchange of fresh air for the birds in the room, they will 

 breathe the air over and over again, and there is a gradual loss 

 of oxygen and an increase in the carbon dioxid content. 



If the amount of oxygen falls from 20 per cent., the amount 

 normally in the air, to 11 per cent, there is noted distressed 

 breathing, and when it falls to 4 per cent, there is rapid asphyx- 

 iation and death. 



Respiration is presided over by the nervous system. The 

 respiratory nerve-center is located in the floor of the fourth 

 ventricle in the medulla oblongata (at the base of the brain). 



Excessive bodily temperature or exertion causes accelerated 

 respiration. The fright caused in handling birds is sufficient in 

 most instances to more than double the number of respirations. 



VENTILATION 



The object of ventilation is to supply pure air to the lungs, 

 to dilute and remove from the hen house the noxious gases 

 off from the lungs and from the fluidy portions of the excreta 

 or droppings evacuated from the bowels. 



It is not considered ventilation if the incoming air is derived 



