IN ANIMAL TISSUES. HARRIS. 263 



II. Materials used in Judging of Reduction by 



Tissues. 

 These may be classified as; — 

 l.(a)Those containing, and (b)those not containing oxygen. 



II. (c)Those which are and (d)those which are not pigments. 



A. Pigments: 1. Containing oxygen: haemoglobin; 

 methaemoglobin; sodium-indigo-disulphonate. 



2. Not containing oxygen: methylene blue; Prussian 

 blue. 



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

 nitrate. 



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



III. Methods of Studying the Reducing Pq-wers 



OF Tissues. 



All the following methods of bringing the pigments and 

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

 or other preparations of tissues have been tried: (a) immer- 

 sing pieces of surviving organs in the test substances; (b) 

 mixing the liquids with aqueous, saline or dilute glycerol 

 so-called "solutions" of reductase; (d) injecting surviving 

 organs with the Prussian blue and gelatine mixture; (e) 

 perfusing this injection mass or, for instance, ferric chloride, 

 through the vascular system of a surviving organ; (f) perfusing 

 the blood-vessels, and obtaining in the case of the kidney, 

 artificial urine, in the case of the liver, artificial bile. 



As might be expected, the method merely of immersing 

 pieces of tissue was by far the least satisfactory. No good 

 results comparable with those got by Dr. Vernon {^^) in the 

 case of oxidase were obtained, but in this respect reductase 

 resembles glycogenase, an undoubted endo-enzyme. 



The routine method followed was to use the press-juice 

 from a Klein's press. This was kept sterile under toluene. 

 Its reducing power gradually declined in energy, until at the 

 end of three months it had vanished. 



