INTERNAL RESPIRATION 



555 



The differences in the gaseous exchange are multiplied by three 

 in order that allowance may be made for the increase in the rate 

 of the flow of blood through the active muscles. 



Hill and Nabarro also investigated the respiratory exchange 

 of the brain by a comparison of samples of blood taken from the 

 carotid artery and the torcula Herophili. The following table 

 gives the average differences between the gases of the blood in 

 the deep femoral vein and the carotid artery, and between those in 

 the torcular Herophili and the carotid artery, of dogs in the condi- 

 tion of morphia anaesthesia, and during the tonic and clonic stages 

 of epileptic fits evoked by the intravenous injection of essential 

 oil of absinthe. 



The figures show that the respiratory exchange of the brain is 

 very low, and is but little increased during the stages of an 

 epileptic fit. The contrast with the muscles is most marked. 



The respiratory exchange of glands may be illustrated by the 

 experiments made by Barcroft ( 28 ) upon the submaxillary gland ; he 

 compared the quantities of oxygen and carbon dioxide in samples 

 of venous blood from the resting gland, venous blood from the 

 active gland, and arterial blood from the femoral artery. The 

 quantity of oxygen taken up from the blood is about 0-25 c.c. 

 per minute in the condition of rest, and O86 c.c. per minute when 

 the activity of the gland has been evoked by stimulation of the 

 chorda tympani nerve ; the corresponding values for the dis- 

 charge of carbon dioxide are 0-27 c.c. and 0-97 c.c. After an 

 injection of sufficient atropin to paralyse the secretory fibres of 

 the chorda tympani, the intake of oxygen by the gland is not 

 increased by stimulation of the nerve ; the output of carbon dioxide, 

 on the other hand, is greatly increased, at least for a time. 



Barcroft's experiments show how complicated are the pheno- 

 mena which have to be investigated. The venous blood which 



