264 RESPIRA TION 



and in luminous insects, like the glow-worm, it has been noticed 

 that the phosphorescence, which is certainly dependent on oxida- 

 tion, begins and is most brilliant in those parts of the cells of the 

 light-producing organ that surround the ends of the tracheae. Micro- 

 scopic evidence has been obtained that the nucleus plays a predomi- 

 nant part in intracellular oxidation e.g., in the indophenol (p. 268) 

 and similar reactions the coloured oxidation products are deposited 

 chiefly in and around the nuclei of such cells as liver and kidney 

 cells and frog's red corpuscles (Lillie). 



The fact observed by Bohr, and already alluded to (p. 252), that 

 an increase in the carbon dioxide tension of blood diminishes its 

 combining power for oxygen," and therefore favours the giving up 

 of oxygen to the lymph and tissues, may have an important influence 

 on internal respiration. The effect is much more marked where the 

 oxygen tension is low than where it is high, so that in the lungs the 

 taking up of oxygen is scarcely interfered with even by a high carbon 

 dioxide tension. Lymph, bile, urine, and the serous fluids contain 

 very little oxygen7~btrt-so much carbon dioxide that the pressure of 

 that gas in all of them is greater than in arterial blood, while in 

 lymph alone (taken from the large thoracic duct) has it been found 

 less than that of venous blood. And it is probable that lymph 

 gathered nearer the primary seats of its production (the spaces of 

 areolar tissue) would show a higher proportion of carbon dioxide. 

 Strassburg found that with a pressure of carbon dioxide in the 

 arterial blood of 21 mm. of mercury, the pressure in bile was 50 mm., 

 in peritoneal fluid 58 mm., in urine 68 mm., in the surface of the 

 empty intestine 58 mm. Saliva, pancreatic juice, and milk, also 

 contain much carbon dioxideT^nH6nly a little, if any, oxygen. 

 From muscle no free oxygen at all can be pumped out, but as much 

 as 15 voTumes per 100 of carbon dioxide, some of which is free 

 that is. is given up to the vacutmT alone while some of it is fixed, 

 and only comes off after the addition of an acid. 



Muscle may be safely taken as a type of the other tissues in regard 

 to the problems of internal respiration. It is instructive, therefore, 

 to observe that the great scarcity of oxygen in the parenchymatous 

 liquids which batjie the tissues, here in the tissues themselves, deepens 

 into actual famine. The inference is plain. The active tissues are 

 greedy of oxygen; as soon as it enters the muscle it is seized and 

 ' fixed ' in some way or other. The traces of oxygen in the lymph 

 cannot therefore be journeying away from the tissue elements; they 

 must have come from another source, and this can only be the blood. 

 Could we gather tissue lymph for anatysis directly from the thin 

 sheets that lie between the blood capillaries and the tissues, we 

 might find more oxygen present as well as more carbon dioxide. 

 But if we did find more oxygen, it would still be oxygen in transit 

 from the capillaries towards places where the partial pressure of 



