236 



EXTENT OF THE RESPIRATORY EXCHANGE OF GASES. 



blood either of non-nitrogenous or of nitrogenous substances. The 

 output of carbon dioxid changes to a certain extent in correspondence 

 with the combustion of these substances by means of a constant quantity 

 of oxygen. 



Hunger greatly reduces the combustive processes in dogs; but in 

 guinea-pigs it produces at most a small reduction in the consumption of 

 oxygen. 



8. The Number and the Depth of the Respirations have practically no 

 influence on the formation of carbon dioxid, or on the oxidation- 

 processes in the body, the latter being regulated rather by the tissues 

 themselves through a mechanism as yet unknown. These factors, 

 however, have been observed to exert an evident influence on the removal 

 of the carbon dioxid already formed in the body. An increase in the 

 number of respirations, the depth remaining the same, as well as an 

 increase in their depth, the number remaining the same, results in an 

 absolute increase in the output of carbon dioxid. The quantity seems 

 relatively diminished, however, when viewed with reference to the 

 amount of gases interchanged. Example: 



Deep respirations, and also artificial respiratory movements, increase the 

 absorption of oxygen into the blood to the point of saturation. Limitation of 

 the supply of oxygen diminishes its consumption in the body in considerably 

 greater measure than does hunger. Naturally, increased activity of the respiratory 

 muscles causes in itself a greater interchange of gases. 



9. Exposure to Light causes an increase in the excretion of carbon 

 dioxid in frogs, mammals, and birds, even in frogs deprived of their 

 lungs or of their cerebral hemispheres, or in those in which the spinal cord 

 has been divided high up. At the same time the consumption of oxygen 

 is increased. The same processes occur in individuals without eyes, 

 though to a more limited extent. Rodents and birds show the maxi- 

 mum in red light, toads in violet light. According to Aducco starving 

 pigeons lose weight more quickly in the light than in the dark. Quincke 

 demonstrated that certain tissues, such as leukocytes and parts of fresh 

 tissues, attract more oxygen to themselves under the influence of light 

 than in the dark. 



The nitrogenous metabolism of animals remains unchanged during exposure 

 to light. The increased output of carbon dioxid is, therefore, to be attributed to 

 an increased transformation of fat; hence, animals accumulate more fat when 

 kept in the dark. 



10. Blood-letting produces no diminution in the respiratory exchange 

 of gases, but does cause an increase in the nitrogenous excretion. Pro- 

 found anemic conditions diminish the interchange of gases. 



11. Changes in the Atmospheric Pressure produce a slight diminu- 

 tion in the interchange of gases if breathing is made easier; but if 



