414 PROCESSES INFERRED FROM DIRECT OBSERVATION 



Sepia. These oxidases are also able to accomplish the oxidation of 

 other hydroxy-aromatic compounds, such as Catechol and Quinol. 



An enzyme which is often mistakenly regarded as an oxidizing 

 enzyme is the Catalase which occurs in nearly all living tissues and 

 which possesses the property of decomposing peroxides, without, 

 however, liberating active oxygen. It is to this enzyme that the 

 frothing of hydrogen peroxide when added to blood or saliva is due. 

 It is in fact a retarder of oxidations and not an accelerator, for it antici- 

 pates the action of peroxidase upon peroxides and decomposes them, 

 thus depriving them of ability to transfer oxygen to oxidizable mate- 

 rials. It is probably to be regarded as a controlling agent or check upon 

 overactivity of oxidizing enzymes. It has been shown by Burge that 

 the catalase-content of different tissues varies very greatly, that of the 

 liver being greatly in excess of the catalase-content of muscular tissues. 

 The curious observation has been made by Burnett, however, that if a 

 small proportion of liver-tissue be mixed with muscle-tissue the power 

 of this mixture to decompose hydrogen peroxide is equal to that of 

 an equal weight of pure liver-tissue. This looks either as if catalase 

 really consists, like the oxidases, of two parts, of which only one is 

 contained in considerable amount in muscle-tissue, or else the catalase 

 in muscle-tissue is present therein, not as such, but in the form of a 

 proenzyme or zymogen, which is activated by liver-tissue. 



BIOLUMINESCENCE. 



The phenomenon of bioluminescence or "phosphorescence" which is 

 displayed by so many organisms, both vegetable and animal, has 

 recently been subjected to very careful study and analysis by N. 

 Harvey. The peculiarity of bioluminescence is the extraordinary 

 intensity of the light which is developed, without any perceptible 

 waste of energy, in the form of heat, an ideal unattainable by any 

 means of illumination at present within our control. The luminescence 

 is dependent upon the occurrence of oxidations, for it disappears when 

 the luminescent system is deprived of oxygen, even when the lumines- 

 cence is made to occur independently of the life of the organism, as in 

 extracts made from the luminous tissues. 



Both Dubois and Harvey, the two leading investigators of this 

 phenomenon, are agreed that the production of luminescence in 

 animal or plant-tissues or tissue-extracts requires the interaction of 

 two substances. The one of these is, according to Harvey, the sub- 

 stance from which the luminescence proceeds, and it is progressively 

 consumed in the process; this he terms the Photogenin. The other 

 substance facilitates the oxidation of the photogenin and is termed by 

 Harvey Photophelein. The photogenin is colloidal, i. e., does not pass 

 through a dialyzing membrane of parchment, and its light-producing 

 ability is destroyed by heating. The photogenin from the luminous 

 crustacean, Cypridina, at all events, appears to be a protein. It is 



