54 SCIENCE PROGRESS 



and it is extremely slow at zero ; inhibition may be induced 

 indefinitely by keeping the mixture ol pigment and juice 

 surrounded by a freezing mixture ; on the mixture being 

 removed to air temperature, reduction goes on as rapidly as is 

 normal for that temperature ; the ferment, therefore, has been 

 inhibited but not destroyed. As the temperature rises, the 

 velocity of reduction increases correspondingly; the optimum 

 temperature is somewhere between 40 and 45 °C. Like 

 recognised enzymes, reductase has a destruction temperature 

 which is in the neighbourhood of 70 °C. 



While fresh juice reduces soluble Prussian blue within a 

 minute or so at room temperature (17 C), its activity rapidly 

 falls off, so that after twenty-four hours it takes some minutes 

 longer to bleach the pigment; yet juice which takes some 

 minutes at room temperature has its time distinctly shortened 

 at 40 c C, the blood heat. There is a decay in the activity of 

 tissue reductase the longer the juice is kept even when it has 

 been covered with a layer of toluene to prevent putrefaction. 

 In a particular series of recent observations extending over 

 a week, the following fall off in activity of reduction of liver 

 juice was estimated. At the end of twenty-four hours the 

 activity had fallen to over 80 per cent, of its original value, at 

 the end of the second day to 66 per cent., at the end of the 

 fourth day to 30 per cent., and at the end of the eighth day to 

 about s per cent. The survival of hepatic reductase to the 

 eighth day is evidently not an isolated phenomenon, for quite 

 recently it has been found that both hepatic xanthinase and 

 uricase are active in liver juice as late as the fifth day. We 

 shall later see that this decrease in activity is amenable to 

 mathematical treatment. 



Since several substances are known to be able to bleach 

 soluble Prussian blue or cause it to fade, we had to eliminate 

 the action of such as could possibly vitiate our results. Alkalies 

 had first to be disposed of. It is of course true that alkalies 

 can cause rapid fading of soluble Prussian blue and certain 

 other pigments, but none of these is present in the living tissues. 

 When all the various inorganic salts present in the blood or 

 lymph had been examined, it was found that none of them 

 caused any fading of the blue beyond what a similar dilution 

 with water would have done. No more effective were mixtures 

 of the salts ; and Ringer's solution itself produced no fading. 



