530 



VETERINARY PHYSIOLOGY 



occurs under conditions when such an acidosis could hardly 

 develop. 



While an increase of free CO., increases the depth, and also 

 generally the rate of breathing, and thus secures a more 

 thorough ventilation of all parts of the lung, oxygen 

 deficiency seems chiefly to cause an acceleration of rate. In 

 consequence of this quicker, more shallow breathing only 

 the more expansile parts of the lung are ventilated (p. 523). The 

 result is that a greater proportion of the blood passes through 

 parts of lung imperfectly ventilated, from the alveoli of 



Giving off of CO^ in hyper- 

 ventilated part of lung. 



Giving off of CO^ normal 

 and actual. • . 



Taking up of O2 by the blood 

 in hyper- ventilated part of lung. 

 Taking up of O2 normal. _ 



Taking up of O2 actual. 



Giving off of 

 COo in non- 

 ventilated 

 part of lung. 



Taking up of 

 Oo in same. 



Fig. 213. — To show effects of shallow breathing and imperfect ventilation 

 of the lungs upon the taking up of Og and giving off of COo. The 

 shaded part of the square represents the badlj' ventilated part. 



which the oxygen gets used up and reduced to a low partial 

 pressure. If the pressure falls below 50 mm. Hg the blood will be 

 imperfectly oxygenated. The rest of the blood passing through 

 the well-ventilated expansile part of the lung cannot take up 

 much more oxygen than it does at a pressure of a little over 

 50 mm. Hg (p. 493), so that any rise in the partial pressure as the 

 result of better ventilation produces only a small effect. Thus 

 imperfectly oxygenated blood is mixed with a smaller quantity 

 of normally oxygenated blood, and thus the total blood leaving 

 the lungs carries less oxygen than normally (fig. 213). 



On the other hand, since the C0„ tension varies directly 

 with the partial pressure, the decreased giving off of COo in 

 the badly ventilated parts of the lung may be compensated for 



