412 THE RESPIRATION 



gland (the chorda tympani) in the dog, it has been found that, whereas 

 the more abundant secretion lasts only so long as the stimulus is ap- 

 plied to the nerve, the 2 consumption is increased to several times that 

 of rest, and remains increased for a considerable period after the stimulus 

 has been removed. Accompanying the increased functional activity 

 there is a very marked increase in bloodflow due to vasodilatation, which, 

 in part at least, is dependent upon the secretion into the blood of some 

 substances resulting from the glandular activities, and is not entirely 

 due to the action of vasodilator nerve fibers. 



Similar results have been obtained in the case of the pancreas when 

 excited to secrete by the injection of secretin (see page 460). Under 

 such conditions, the oxygen consumption has been observed to increase 

 about fourfold and to be accompanied by a dilatation of the gland. 



The work on the kidney has been especially interesting, because it 

 has been found that increased activity, which of course is measured by 

 the rate of urine excretion, is not always accompanied by increased 

 consumption of oxygen. When diuresis is caused by injecting Ring- 

 er's solution into the circulation, a great increase in urine outflow may 

 occur without any change in oxygen consumption ; whereas, on the other 

 hand, when a diuretic such as sodium sulphate or caffeine is used, the 

 oxygen consumption increases enormously. 



Regarding the other tissues and organs, the 2 consumption of the 

 lungs and brain appears to be small. It is a very significant fact, how- 

 ever, that the higher cerebral centers are extremely sensitive to depri- 

 vation of 2 . 



The Blood. In the blood itself, a certain amount of oxidation goes 

 on because of the presence of living cells such as the blood corpuscles. 

 This oxidation becomes considerable in the blood of animals rendered 

 anemic by the injection of phenyl hydrazin. A thorough investigation 

 of the cause of this greater oxidation has shown it to be owing, not to 

 an increase in nucleated erythrocytes, but to the presence of the young 

 unnucleated red blood corpuscles, which appear in large numbers in the 

 blood under these conditions. A similar increase in blood oxidation oc- 

 curs during posthemorrhagic anemia the rate of oxidation running paral- 

 lel with the rate of regeneration of the red corpuscles. 



The Mechanism by Which the Demands of the Tissues for 

 Oxygen Are Met 



There are two possible methods by which this may be brought about: 

 (1) by a change in the C H or the saline constituents or the temperature of 

 the plasma, so that the hemoglobin more readily delivers up its load 



