4:66 RESPIKATION. 



venous blood. It is not absolutely certain whether the ni- 

 trogen which exists in the blood is derived from the air or 

 from the tissues. Its almost constant exhalation in the ex- 

 pired air would lead to the supposition that it is produced in 

 small quantity in the system, or supplied by the food. Ac- 

 cording to Bernard, the quantity of nitrogen in the arterial 

 blood is from two to five parts per thousand, but it is present 

 in very much larger quantity in the venous blood. 1 There 

 is no evidence that nitrogen enters into combination with the 

 blood-corpuscles; it exists simply in solution in the blood, 

 which is capable of absorbing about ten times as much as 

 pure water. 2 Nothing is known with regard to the rela- 

 tions of the free nitrogen of the blood to the processes of 

 nutrition. 



Condition of the Gases in the Blood. It is now pretty 

 generally admitted that the oxygen of the blood exists, not 

 in simple solution, but in a condition of feeble combination 

 with certain of the constituents of the blood-corpuscles. 3 It 

 is clearly demonstrated that the corpuscles are the elements 

 which fix the greatest quantity of this gas. Carbonic oxide, 

 which has a great affinity for the corpuscles, displaces almost 

 immediately all the oxygen which the blood contains. When 

 the corpuscles are destroyed, as they may be readily by re- 

 ceiving fresh blood into a quantity of pure water, the red 

 color is instantly changed to black. Oxygen in the blood 

 bears a closer relation to the corpuscles than that of mere solu- 



I Unpublished lectures delivered at the College of France in the summer 

 of 1861. 



II MAGNUS, loc. cit. 



3 It is not settled which of the constituents of the blood-corpuscles has the 

 greatest affinity for oxygen. It has been supposed to be combined especially with 

 the coloring matter ; but experiments on this point are contradictory. Lehmann 

 noticed no difference in the color of a solution of blood-crystals treated with oxy- 

 gen, and the same solution treated with carbonic acid ; the only difference was 

 that the latter became turbid (Physiological Chem., Am. ed., vol. i., p. 573). 

 Meckel made some experiments in which " hsematoglobulin " was changed to a 

 bright red by oxygen, and to a bluish red by carbonic acid (Ibid., p. 574). 



