THE BIOCHEMISTRY OF RESPIRATION 267 



excited to abnormal metabolism by mechanical injuries, for the 

 finer the state of division of a tissue the less is its respiratory 

 power. 1 The respiratory processes did not cease altogether 

 in an hour or so, but a smaller " accessory respiration " remained 

 and might persist for some hours. The C0 2 output of this 

 respiration was considerably smaller than the oxygen intake, 

 and if the tissue had previously been heated to 70° it ceased 

 altogether, though a moderate absorption of oxygen continued. 

 This accessory respiration was due partly to soluble tissue 

 constituents, for Warburg 2 found that if an aqueous extract 

 of liver were filtered through a Berkefeld filter, it retained 

 about 4 per cent, of the respiratory powers of the intact liver, 

 whilst an unfiltered extract, containing minute particles in 

 suspension, had about 20 per cent, the respiratory power. 

 These extracts produced C0 2 in addition to absorbing oxygen, 

 or exhibited a genuine respiratory process. Accessory respira- 

 tion may continue for as long as three days in intact tissues, 

 for the writer 3 found that small quantities of C0 2 continue to 

 be evolved for this length of time by kidneys perfused with 

 1 per cent. NaF. 



Freshly minced muscle, liver, and kidney are able to oxidise 

 citric, fumaric, and malic acids, apparently to the C0 2 -f H 2 

 stage, but these powers appear to be bound up with the con- 

 tinued vitality of the cells, and cease when the "chief respira- 

 tion " ceases. 4 This chief respiration is itself dependent to a 

 considerable extent on soluble constituents of the tissues, for if 

 freshly minced liver, kidney, or muscle is extracted with water 

 it loses most of its respiratory powers, but it regains them 

 on addition of the extract. These soluble constituents, called 

 by Battelli and Stern 5 " pnein," probably consist for the most 

 part of easily oxidisable organic acids They are not destroyed 

 by boiling, or by proteolytic enzymes. 



It will be realised that the processes of tissue respiration which 

 begin with the absorption of oxygen and end with the production 

 of C0 2 and H 2 are of all degrees of complexity and possess 



1 Harden and Maclean, Joum. Physiol. 43, p. 34, 191 1. 



1 Warburg, Arch. f. d. ges. Physiol. 154, p. 599, 191 3; but cf. Harden and 

 Maclean, I.e. 



3 Vernon, Joum. Physiol. 35, p. 78, 1906. 



4 Battelli and Stern, Biochem. Zeit. 31, p. 478, 191 1. 



5 Battelli and Stern, ibid. 33, p. 315, 1911. 



