270 EXISTENCE OF A REDUCING ENDO-ENZYME 



phenomena of the fading of pigments in contact with proteins 

 which I have called "the Creighton effects," I still believe 

 that vital reduction is something distinct from these and is 

 probably enzymic. 



VII. Indications That a Tissue Endo-Enzyme exists 



1. The first consideration regarding reduction being due 

 to an enzyme is that, whereas quite fresh juice vigorously and 

 older juice more gradually reduces several different kinds of 

 chemical substances, boiled controls do not do so at all. 



2. The behaviour of the juice in regard to temperature 

 is the next point indicating the presence of an enzyme. 



Its optimum is between 42° C and 46° C. Thus Herter 

 found reduction processes were accelerated in the experi- 

 mentally induced fever of hog cholera. As the temperature 

 falls, the rate of reduction is diminished until at zero reduction 

 is entirely inhibited. But at a temperature as low as minus 

 14°C, the reducing power is not destroyed; it is merely kept in 

 check. 



I have kept under observation a mixture of absolutely 

 fresh liver-juice and Prussian blue, surrounded by a freezing 

 mixture for 24 hours, without noticing the least degree of 

 fading of the deep blue colour. On removing the tube from the 

 freezing mixture the colour was completely discharged by the 

 time the juice had reached room-temperature (17°C). 



Herter found in the intact animal that "the power of 

 reduction was much diminished by cold." 



A typical experiment may be quoted in connexion with 

 temperatures. 



Three water baths were brought to (a) between 40° and 

 41°C; (b) between 42°C and 43°C; and (c) between 44° and 

 45° C respectively. In each bath a tube was placed containing 

 3 c.c. of 24 hours old hepatic juice shaken up with 20 c.c. of 

 Prussian blue all under toluene. In 6 hours the tube in (a) 

 was green, that in (b) was green-white, the one in (c) was 



