BODY TISSUES AND FLUIDS 455 



derson, and application inado to the blood gases by Henderson and Smith. 

 Very recently Van Slyke and Stadie have introduced a number of dif- 

 ferent refinements in the Van Slyke method of gas analysis and it would 

 seem that this method now left little to be desired in the point of accuracy. 



The great practical importance of a knowledge of the factors concerned 

 in the carrying of oxygen to the tissues and the removal of carbon dioxid 

 is apparent. 



Oxygen. As lias already been pointed out, the ability of the blood 

 to absorb and take up oxygen depends upon its hemoglobin content. Since 

 hemoglobin so readily takes up and gives off oxygen, it is obvious that 

 venous blood should be partly unsaturated and therefore differ from the 

 arterial blood in respect to its oxygen content, and further that blood 

 obtained from different parts of the venous system should differ in its 

 oxygen unsatu ration. Extensive studies on the venous blood from single 

 organs have been made in animals by Barcroft and his associates, but in 

 the human adult the superficial veins of the limbs and neck, particularly 

 of the arm (vena mediana), are the only sources from which venous blood 

 can be obtained. This means that in the human only blood coining from 

 a limited region, consisting chiefly of muscles, can be studied. 



Lunsgaard(a) has given the following figures for the oxygen content 

 and oxygen unsaturation of the venous blood of the normal resting adult. 

 The results are the average of thirty-eight determinations on twelve indi- 

 viduals and are given in tabular form below: 



In studying this question on circulatory disorders, Lurisgaard(fr) found 

 that in twelve patients with compensated heart lesions the unsaturation 

 i'ell within normal limits, between 2.5 and 8 volume per cent, while in 

 four patients with uncompensated heart disease the values for the un- 

 saturation were all above the normal limits, from 9.7 to 15.2 volume per 

 cent. In these cases the oxygen unsaturation appears to afford an objective 

 criterion of the positive effect of digitalis therapy. From studies per- 

 formed on patients with varying amounts of hemoglobin it has been shown 

 that the oxygen unsaturation of the venous blood is independent of the oxy- 

 gen capacity, unless the latter is reduced below the normal value for oxygen 

 unsaturation (about 5 volumes per cent). Lunsgaarcl found, for example, 

 that in a polycythemic patient with an oxygen capacity of 3-3.4- volumes 

 per cent, the venous oxygen unsaturation was 5.4 volumes per cent, while 



