EXTRINSIC MECHANISMS OF SECRETION 273 



more recent experiments by Barcroft, it may in the dog be set 

 down as amounting to more nearly six times 'the blood-supply 

 in the resting condition. 



Comparative analyses of the blood-gases in the arterial blood 

 and the venous blood passing from the gland show also, according 

 to Barcroft's experiments, that the amount of oxygen used by 

 the gland, and also the amount of carbon dioxide formed, as shown 

 by the sum of the increase in the venous blood and the amount 

 in the saliva, both increase during activity much above the 

 amounts similarly determined in the case of the resting gland, 

 pointing to increased chemical activity during secretion. 



Thus, Barcroft found that during secretion of saliva by the 

 submaxillary gland, induced by stimulation of the chorda tympani, 

 the oxygen taken from the blood was increased to an amount which 

 was three to four times that taken up by the resting gland. The 

 carbon dioxide given out by the gland was also increased under 

 the same circumstances to an equal or even greater amount. While 

 after an injection of atropin sufficient to cause paralysis of the 

 secretion the intake of oxygen was not increased by stimulation 

 of the chorda tympani, on the other hand the output of carbon 

 dioxide was increased, at least for a time. 



In the case of the pancreas Barcroft and Starling found that 

 the secretion was also accompanied by an increased oxygen absorp- 

 tion from the blood, and that this increased oxidation took place 

 irrespective of increased blood-flow through the organ. These 

 observers also found that the normal oxidation in the pancreas 

 was much greater than in the body generally, and about the 

 same as that of the submaxillary gland. 



In experiments upon the metabolism in the kidney, Barcroft 

 and Brodie found that the production of diuresis was accompanied 

 by a marked increase in the absorption of oxygen, although there 

 was no direct proportionality in oxygen absorption and degree 

 of diuresis. The authors found no definite relation between the 

 oxygen taken in and the carbon dioxide given out, and also that 

 the onset of diuresis was not necessarily accompanied by an increase 

 in the rate of blood-flow through the kidney, and even where an 

 increased flow was found it was never proportional to the accelera- 

 tion of the urinary flow. 



18 



