224 STUDIES IN ADVANCED PHYSIOLOGY. 



the oxygen will continue to stream into the plasma until the 

 pressure in the plasma reaches three pounds, and then 

 everything will come to a standstill. Of course at this 

 juncture the blood is pushed onward into the pulmonary 

 veins and is as arterial blood sent back to the left side of 

 the heart, to be, of course, in the lung replaced by fresh 

 venous blood from the pulmonary arteries. 



By way of summary the condition of things in this 

 arterial blood as it leaves the lungs is re-stated. The 

 plasma of the arterial blood has oxygen dissolved in it to 

 a pressure of three pounds to the square inch, or at least 

 not very far from that. All the haemoglobin has been 

 changed into oxyhaemoglobin, and as this oxyhsemoglobin 

 is in the plasma surrounded by an oxygen pressure of moi;e 

 than half a pound it does not disunite with its oxygen. In 

 this condition of things the blood is sent out through the 

 arteries over the entire body and finally reaches the capil- 

 laries in the tissues. This is the seat of the internal 

 respiration. 



THE PHENOMENA OF INTERNAL EESPIEATION. 



1. The Oxygen Supply. In order here, also, to more 

 thoroughly understand just what takes place in this gaseous 

 interchange, let us picture the exact condition of things in 

 the tissues. The arterial blood, as described, is in the tis- 

 sue capillaries. Just outside of the capillaries lies the 

 lymph which bathes the tissues, and in which lie the live 

 cells of the body, the units for which the nourishment of 

 the blood and the oxygen which it carries are intended. 

 These cells immersed in the lymph have a great avidity for 

 oxygen, and use it up as fast as it is carried to them. Stat- 

 ing this in a more scientific way, there is in the lymph, 

 bathing healthy tissues, never much free oxygen, and of 

 course there can then be no oxygen pressure. We have the 

 lymph with no oxygen pressure in it, separated from the 

 plasma of the blood which has a three-pound pressure, by 

 a thin capillary wall. It was pointed out in discussing 



