390 PHYSIOLOGY. 



Irritation of the vagus increased the absorption of oxygen. In the 

 warm-blooded animal irritation of the vagus increased the absorption of 

 oxygen and the exhalation of carbon dioxide. 



But how does the burning of carbon take place at the temperature 

 of the body ? Outside of the body the carbon will not be oxidized at 

 the body temperature, but inside the tissues it is. This contradiction 

 is explained by the presence of ferments, oxidases, which in the test 

 tube certainly generate these oxidations, and probably also do so in 

 the tissues. 



In the living animal experiments have been made to determine 

 the respiratory exchanges in different tissue. Chauveau and Kauf- 

 mann, in 1887, found by a comparison of the arterial blood going to 

 the muscle elevating the upper lip of the horse and the venous blood 

 coming from it, the following numbers : 



Quantity Per Minute and Per Kilogram of Muscle. 



2 absorbed CO 2 given off Respiratory Quotient 



Repose 0.0068 gr. 0.0068 gr. 1 



Work 0.140 gr. 0.245 gr. 1.75 



They also made similar studies upon the parotid gland and ob- 

 tained similar results. These experiments show the actual state of 

 respiration in the tissues. The carbonic acid is formed in the tissues 

 and thrown oif by the lungs. Carl Vierordt, with a rubber band about 

 his finger and a spectroscope for direct vision, saw the two bands in 

 the spectrum of oxyhsemoglobin in the end of the finger gradually 

 vanish and the single band of haemoglobin appear. He found this to 

 take place in two minutes, the time required for the tissues to consume 

 the oxygen of the haemoglobin in the blood retained at the end of 

 the finger. This experiment demonstrated the avidity of the tissue 

 for oxygen. 



The blood itself has a very feeble oxidation when compared with 

 other tissues. Zuntz cut the nerve in the leg of a dog and found that 

 the exchange of gases was reduced. The lessening of oxygen used up 

 and of carbonic acid given off was about the same in amount. 



The question arises, How far are the carbon dioxide producing 

 powers and oxygen absorbing powers of living tissue dependent upon 

 one another? All the results of experiment show that the processes 

 of tissue oxidation take place in more than one stage, and that the 

 earlier stages are more readily accomplished than the final stage which 

 leads to the production of free carbon dioxide. 



To study tissue respiration it is incumbent to analyze the blood 



