[HARRIS] A REDUCING ENDO-ENZYME. 127 



grey matter of central nervous system all reduced the blue to the leuco 

 state. An animal which was chilled by wet cloths or ice ' 'exhibited 

 the powers of reduction much diminished by cold". Herter showed 

 that, conversely, the reducing power of the tissues of an aminal injected 

 with the microorganisms of a specific fever was increased. 



Underhill and Clossoni" in 1905 confirmed Herter 's views and 

 came to the conclusion that their experiments demonstrated the simul- 

 taneous action of both oxidative and reducing processes in the animal 

 organism. 



In 1906 Professor J. C. Irvine and I" showed that the intra vitam 

 reduction of Prussion blue was not a deoxidation, but the removal 

 of an ionic charge. 



By perfusing the surviving kidney of a sheep with the Prussian 

 blue mixture, I obtained from the ureter an absolutely colourless 

 artificial urine which was blued immediately on treatment with HjOj. 



Authors with increasing frequencj^ are recognising the existence 

 of reductase. 



Pppenheimer^-, for instance, in his large work on "Ferments" 

 does so: most of the authors of text-books mention the reducing 

 power of tissues even when they do not recognise "reductase". 



Some, however, frankly postulate a reducing ferment, thus G. P. 

 Mudge^^ writes, ' 'If an albino does carry a chromogenous body which 

 only needs the influence of an oxidising or reducing ferment to cause 

 it to produce pigment", etc. 



// Materials used in Judging of Reduction by Tissues. 



These may be classified as: — 



I. Those containing, and those not containing oxygen. 



II. Those which are and those which are not pigments. 



A. Pigments: 1. Containing oxygen, haemoglobin; methaemo- 

 globin; sodium-indigo-disulphonate. 



2. Not containing oxygen; methylene blue; 

 Prussian blue. 



B Non-pigments: 1. Those with oxygen, e.g., sodium nitrate. 



2. " without oxygen, e.g., ferric chloride. 



///. Methods of Studying the Reducing Powers of Tissues. 



All the following methods of bringing the pigments and other 

 substances into contact with the tissues or tissue-juices or other prep- 

 arations of tissues have been tried: (a) immersing pieces of surviv- 

 ing organs in the test substances; (b) mixing the liquids with the 

 press-juice of disintegrated organs; (c) mixing the liquids with aque- 



