THE MECHANISM OF TISSUE RESPIRATION 173 
the more rapid the metabolism. This view can be combined 
with that of Pfliiger, 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. Chen. 15, p. 335 (1891); 17, p. 311 (1893); 19, p. 422 
(1894). 
AUBERT, Pfliigers Arch. 26, p. 293 (1881). 
BAGLIONI, Zezt. f. allgem. Physiol, 4, p. 384 (1904). 
BaRcroFt, Journ. Physiol. 27, p. 43 (1901). 
— and BropIik, Journ. Physiol. 32, p. 18 (1904) ; 33, p. 52 (1905). 
BERNARD, “ Lecons sur les Phenomenes de la Vie,” vol. ii. p. 190 (Paris, 1879). 
BUCHNER and MEISENHEIMER, Berichte, 37, p. 417 ; 38, p. 620. 
DETMER, Jahrbicher f. wiss. Botanik, 12, p. 237 (1879). 
ENGELMANN, Jenaische Zeit. f. Med. u. Naturw. 4, p. 321 (1868). 
FLETCHER, Journ, Physiol, 23, p. 10 (1898) ; 28, pp. 354 and 474 (1902). 
and HoPKINS, Journ. Physiol, 35, p. 247 (1907). 
VON FREY and GRUBER, A7ch. f. (Anat. u.) Physiol. 1885, p. 519; also VON 
FREY, /oc. cit. p. 533- 
FROHLICH, Ze7t. f. allgem. Physiol. 3, p. 131 (1903). 
HERMANN, “Untersuch. ii. d. Stoffwechsel d. Muskeln ” (Berlin, 1867). 
Lowy, Pftiiger’s Arch. 58, p. 409 (1894). 
MEYER, Arch. f. exp. Path. u. Pharm. 1%, p. 304 (1883). 
