THE MECHANISM OF TISSUE RESPIRATION 169 



by an accumulation of lactic acid, especially in the liver : also 

 those of Araki, who showed that lactic acid appeared in the 

 urine of animals poisoned by carbon monoxide, phosphorus, or 

 arsenic. 



The writer has obtained further evidence of the incom- 

 pleteness of tissue oxidation under abnormal conditions by 

 experiments upon excised mammalian kidneys. When these 

 organs are perfused with oxygenated Ringer's solution for ten 

 or twelve hours, their vitality gradually diminishes, but the 

 processes of tissue oxidation, though gradually becoming feebler 

 in magnitude, do not lack completeness, and the respiratory 

 quotient remains practically constant at about "85. Kidneys 

 which previous to perfusion have been heated for half an 

 hour to 50 to 6o°, or frozen solid and thawed, or been kept 

 in a moist chamber for three to nine days after excision, or 

 poisoned by hydrocyanic acid, likewise show considerable 

 diminution in their gaseous metabolism, but the processes of 

 tissue oxidation still remain complete, and the respiratory 

 quotient keeps at about '85. When, on the other hand, a kidney 

 was perfused with oxygenated saline solution containing 

 •06 to "io per cent, of lactic acid, or '005 to "025 per cent, of 

 free ammonia, its oxygen-absorption power rapidly dimin- 

 ished, but its C0 2 -producing power fell off more rapidly still, 

 so that after four to eight hours of perfusion its respiratory 

 quotient dropped to -46- 36, i.e. to about half the normal. 



All the experimental evidence available tends to show, there- 

 fore, that the processes of tissue oxidation take place in more 

 than one stage, and that the earlier stages are more readily 

 accomplished than the final stage which leads to the production 

 of free C0 2 . How numerous or complex these stages are we 

 have no definite means of knowing, but it is by no means 

 improbable that they are of a comparatively simple nature. It 

 is well known that increased functional activity of muscles or 

 other organs, though it may lead to a tenfold increase of oxygen 

 absorption and C0 2 production, has no effect whatever upon their 

 nitrogenous metabolism. Hence Verworn supposes that only 

 non-nitrogenous groupings or side chains in the " biogen 

 molecules" of the protoplasm are concerned in the ordinary 

 processes of tissue respiration, and he suggests that these side 

 chains may be carbohydrate groupings of an aldehyde character. 

 Also he supposes that intramolecular oxygen is stored up in the 



