PROGRESS IN ANATOMY AND PHYSIOLOGY 



occurs, of which carbonic acid is a chief product. But 

 now that attention had been called to the importance of 

 the ultimate cell, this misconception could not long hold 

 its ground, and as early as 1842 Liebig, in the course of 

 his studies of animal heat, became convinced that it is 

 not in the lungs, but in the ultimate tissues to which 

 they are tributary, that the true consumption of fuel 

 takes place. Reviving Lavoisier's idea, with modifica- 

 tions and additions, Liebig contended, and in the face 

 of opposition finally demonstrated, that the source of 

 animal heat is really the consumption of the fuel taken 

 in through the stomach and the lungs. He showed 

 that all the activities of life are really the product of 

 energy liberated solely through destructive processes, 

 amounting, broadly speaking, to combustion occurring 

 in the ultimate cells of the organism. 



Further researches showed that the carriers of oxy- 

 gen, from the time of its absorption in the lungs till its 

 liberation in the ultimate tissues, are the red corpuscles, 

 whose function had been supposed to be the mechanical 

 one of mixing of the blood. It transpired that the red 

 corpuscles are composed chiefly of a substance which 

 Kiihne first isolated in crystalline form in 1865, and 

 which was named haemoglobin a substance which has 

 a marvellous affinity for oxygen, seizing on it eagerly 

 at the lungs, yet giving it up with equal readiness when 

 coursing among the remote cells of the body. When 

 freighted with oxygen it becomes oxy haemoglobin, and 

 is red in color ; Avhen freed from its oxygen it takes a 

 purple hue; hence the widely different appearance of 

 arterial and venous blood, which so puzzled the early 

 physiologists. 



This proof of the vitally important role played by the 



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