396 THE RESPIRATION 



the heart is becoming overtaxed that it is losing its efficiency. The 

 same result occurs when the heart is dying, and when depressing drugs 

 are used, such as chloral hydrate, potassium cyanide, veratrine, etc. 

 Some other drugs, however, such as epinephrine, do not cause altera- 

 tion in the ratio, nor does vagus stimulation. Of course when the vagus 

 is stimulated, the 2 consumption in a given period decreases because 

 the heartbeats are slowed ; but the absorption of 2 is not increased rela- 

 tively to the slowing of the heart. 



Glands. Most work has naturally been done 011 the most accessible 

 gland the submaxillary. By stimulating the secretory nerve of this 

 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 in 

 such structures as muscles, 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 425). Under 

 such conditions, the oxygen consumption has been observed to increase 

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



The w r ork 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 ahvays accompanied by increased 

 consumption of oxygen. When diuresis is produced 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 0._, 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 leucocytes. This oxidation becomes con- 

 siderable 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 

 corpuscles, but to the presence of the young unmicloated fed blood 



