THE GASES OF THE BLOOD 



255 



the bicarbonate intact, while removing nearly all the rest of the 

 carbon dioxide, the compounds of the gas with organic constituents 

 of the blood being more easily dissociated than the bicarbonate. 

 The best known of these compounds is that which carbon dioxide 

 seems to form with haemoglobin. A solution of haemoglobin absorbs 

 more of the gas than water, and the quantity taken up is not pro- 

 portional to the pressure. There is also evidence of the existence' 

 of dissociable combinations between carbon dioxide and the proteins 

 of the plasma, by which considerable amounts of the gas can. be 

 bound at such carbon dioxide tensions as normally exist in blood. 



In the red corpuscles a portion of the carbon dioxide is in com- 

 bination with alkalies. We know that the corpuscles contain more 

 alkali than the serum, and the titratable alkalinity of ' laked ' 

 blood (pp. 25, 28) is greater than that of unlaked blood, unless 

 a long time is allowed in the case of the latter for the alkalies of the 

 corpuscles to reach the acid used in titration. /The haemoglobin of 

 the corpuscles holds a portion of the carbon dioxide in weak com- 

 bination. ( 



Although the student is warned not to give too much weight to 

 the actual numbers, the present position of our knowledge in regard 

 to the distribution and condition of the carbon dioxide of the blood 

 may be summed up by quoting the calculation of Loewy, that in 

 100 c.c. of arterial blood containing (with a carbon dioxide tension 

 of 30 mm. of mercury) 40 c.c. of carbon dioxide, there are 



When blood is saturated with carbon dioxide and then separated into 

 scrum and clot, the serum is found to yield more gas than the clot ; but 

 if the serum and clot are separately saturated, the latter takes up more 

 carbon dioxide than the former. From this it is argued that a substance 

 combined with carbon dioxide must in blood saturated with the gas pass 

 out of the corpuscles into the serum. The corpuscles at the same time 

 gain water and become larger. The molecular concentration (p. 420) 

 of the serum of defibrinated blood, as measured by the lowering of the 

 freezing-point, increases when it is saturated with carbon dioxide. On 

 the other hand, when blood is saturated with oxygen, the corpuscles 

 lose water and shrink in volume, while the molecular concentration of 

 the serum is diminished. Hamburger has extended these observations 

 to the circulating blood, and has shown that the plasma of venous 

 blood has a higher percentage of alkali, protein, sugar, and fat than 

 the plasma of arterial blood, and that the corpuscles have a greater 

 volume, though not a greater diameter. He therefore supposes that in 

 the pulmonary capillaries, under the influence of oxygen, water passes 

 into the plasma from the corpuscles. In the systemic capillaries the 

 blood becomes loaded with carbon dioxide, and therefore the corpuscles 



