RESPIRATION 



423 



are many reasons for believing that it is continually passing into them by way 

 of the lymph-stream. Its rapid disappearance would indicate that it is 

 immediately utilized for the production of carbon dioxid (which is improb- 

 able on other grounds) , or that the tissues possess a capacity for oxygen storage, 

 of placing it in reserve under some combination or other, by which it can be 

 securely retained until required for oxidation purposes. This is rendered 

 probable from the fact that the carbon dioxid evolved at any given moment 

 is not necessarily dependent on the oxygen just absorbed, for if oxygen be 



Atmospheric Air. 



Ox-iss .m,.Hff , or 20.85 per ce?tt , 



COy - 0.3 7?t m tiff, or 0. 04 joer cen t, 



of an atmosphere. 



//) \Vx-TensiotL (\\ 



3 8 mm 



S per cent. 



C0 z -7ensio?t- 

 337* Hg, 

 6 per cent. 



14-percent. 



Alveolus 



Venous 



Arterial 

 Stood. 



O.OOm?n,Jfff, 

 COSTension lSh68m. 

 6 to 9 percent 



Ox-Tension 



-CO* -Tension 



1<O7wn Jftf, 



3 per cent. 



Tissues. 



FIG. 194. DIAGRAM SHOWING THE RELATIVE TENSION OF OXYGEN AND CARBON DIOXID IN 



THE LUNGS, IN THE BLOOD, AND IN THE TISSUES. 



withheld from a nutritive fluid which is being artificially circulated through 

 a recently isolated organ, carbon dioxid will continue to be discharged for 

 some time. A muscle, or even a living animal e.g., a frog placed in an 

 atmosphere of pure nitrogen will remain active and evolve CO 2 even for 

 several hours. 



Naturally the absorption of oxygen and the discharge of carbon dioxid 

 and the changes of composition which are incident to nutrition will be most 

 marked in those tissues characterized by the greatest degree of physiologic 

 activity. Muscle-tissue exhibits these changes to a greater degree than 

 bone. Tissues with intermediate degrees of activity should exhibit corre- 

 sponding degrees of respiratory change. Experiment confirms this view. 

 Thus, loo grams each of muscle, spleen, and broken bone from a recently 



