THE MECHANISM OF TISSUE RESPIRATION 173 



the more rapid the metabolism. This view can be combined 

 with that of Pfluger, only we must suppose that in the tissues 

 of mammals the restitution of intramolecular oxygen occurs 

 more rapidly and at lower tensions than in those of lower 

 animals. It is very probable that the great difference observed 

 is due chiefly to the difference of temperature. At 37 the 

 processes connected with the absorption and chemical combina- 

 tion of the intramolecular oxygen would doubtless occur more 

 rapidly than at 19 , which is the temperature at which most of 

 Thunberg's experiments were carried out. 



Into the question of oxygen absorption in relation to 

 functional activity I do not propose to inquire. We know, for 

 instance, that an active submaxillary gland absorbs oxygen 

 more than three times as fast as a resting gland (Barcroft), an 

 active kidney more than twice as fast as a resting kidney 

 (Barcroft and Brodie), but we are absolutely ignorant of 

 the inner mechanism by which a nervous or chemical stimulus 

 induces an increase of tissue metabolism. In all probability the 

 chemical changes occurring in the tissues of the active glands 

 are of the same character as those in the resting glands, only 

 they take place at a more rapid rate, just as they take place 

 more rapidly at a higher than at a lower temperature. 



References 



Araki, Zeit. f. physiol. Chem. 15, p. 335 (1891) ; 17, p. 311 (1893); 19, p. 422 



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 AUBERT, Pfliiger 3 s Arch. 26, p. 293 (1881). 

 Baglioni, Zeit.f. allgem. Physiol. 4, p. 384 (1904). 

 Barcroft, Journ. Physiol. 27, p. 43 (1901). 



and Brodie, Journ. Physiol. 32, p. 18 (1904) ; 33, p. 52 (1905). 



Bernard, " Lemons sur les Phenomenes de la Vie," vol. ii. p. 190 (Paris, 1879). 

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Von Frey and Gruber, Arch. f. (Anal, u.) Physiol. 1885, p. 519; also Von 



Frey, loc. cit. p. 533. 

 Frohlich, Zeit.f. allgem. Physiol. 3, p. 131 (1903). 

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