604 PHYSIOLOGY OF RESPIRATION. 



of dissociation in the body. The results obtained by Loewy are 

 indicated in the curve of dissociation shown in Fig. 246, obtained 

 from experiments on human blood. At a pressure of oxygen of 

 152 mms. that is, when exposed to ordinary air the hemoglobin 

 is nearly or completely saturated with oxygen. If the oxygen 

 pressure is increased, if, for instance, the blood is exposed to pure 

 oxygen (pressure, 760 mms.), no more oxygen is combined 

 chemically by the hemoglobin. Additional oxygen will be taken 

 up by the blood, but only in so far as it can pass into solution in the 

 blood-plasma. Oxygen thus dissolved in the blood-plasma obeys 

 the Henry-Dalton law and will be at once given off when the oxygen 

 pressure of the surrounding medium is lowered. If the pressure 

 of oxygen falls below that of the air (152 mms.) the chemically 

 combined oxyhemoglobin begins to dissociate slowly at first, but 

 as the pressure falls below 70 mms. the dissociation becomes 

 much more rapid, and the oxygen thus liberated from chemi- 

 cal combination is from a quantitative standpoint much more 

 important than that freed from solution in the plasma. This, in 

 fact, is the process that takes place as the blood circulates through 

 the tissues. The arterial blood enters the capillaries with its 

 hemoglobin nearly saturated with oxygen, about 19 c.c. to each 

 100 c.c. of blood. After it leaves the capillaries the venous blood 

 contains only about 12 volumes of oxygen to each 100 c.c. of blood. 

 In the passage of the capillaries, which takes only about one second, 

 the blood loses, therefore, 35 per cent, or more of its oxygen. The 

 physical theory of respiration furnishes data to show that this loss 

 is due to a dissociation of the oxyhemoglobin, owing to the fact that 

 in passing through the capillaries the blood is brought into exchange 

 with a surrounding medium lymph, cell liquid in which the 

 oxygen pressure is very low. 



Condition of the Carbon Dioxid in the Blood. Carbon 

 dioxid is evidently contained in the blood in chemical combination 

 as well as in solution. The amount present, 40 to 45 volumes per 

 cent., is entirely too great to be accounted for by solution alone. 

 Moreover, the content of the blood in C0 2 does not vary proportion- 

 ally to the pressure of C0 2 in the surrounding medium in accordance 

 with the law of Henry and Dalton. Examination of the blood by 

 means of the gas pump shows that C0 2 is contained in both the 

 corpuscles and the plasma or serum. The results of various analyses 

 would indicate that about J of the total amount is held in the cor- 

 puscles and about f in the liquid of the blood, and, since the cor- 

 puscles make up about % of the bulk of the blood, this fact would 

 indicate that the C0 2 is distributed uniformly throughout the mass 

 of the blood. The condition of the C0 2 in the blood may be con- 

 sidered under three heads: (1) The part in solution; (2) the part in 



