158 



Chapter X 



difference of pressure which for the sake of simplicity of expres- 

 sion I will call the "final capillary pressure-head." To what extent 

 have the effects of (1) rise of body temperature, (2) the presence 

 of salts in the blood, and (3) the presence of CO 2 , contributed so as 

 to admit of the reduction of the blood at a higher pressure? We 

 may take these in any order. Each of these factors temperature, 

 salts and CO 2 has a general and a local effect, a general effect 

 because the whole blood of the body is at 37 C. and is impregnated 

 with salts and C0 2 , and a local effect because the blood in the capil- 

 laries rises in temperature, acquires carbonic acid, and in some cases 

 at all events alters in its saline content as it traverses the tissue. 



100 



10 20 30 40 50 60 70 80 90 100 



It will be best to consider the general effects of temperature, 

 salts and acids first. Let us take them in reference to the case 

 described above. Rise of temperature does not alter the mathe- 

 matical form of the curve, it merely alters the scale on which it is 

 drawn. From Fig. 85 which we have just been considering we can 

 see the effect of temperature : haemoglobin at 38 C. when 50 % 

 reduced is in equilibrium with oxygen at a pressure of about 7'5 mm. 

 of mercury ; this then becomes the " final capillary pressure-head," it 

 is twenty-five times higher than it would have been at 16 C., hence 

 oxygen can diffuse at 7*5 mm. pressure at least out of the vessels into 



