542 OXIDATION FERMENTS 



the lowering of pressure within an enclosed system). 11 This 

 method has been improved by H. H. Bunzel in Washington ; 

 in the latter 's method the containers are fastened to a shak- 

 ing apparatus placed in a thermostat and the changes in 

 pressure occasioned by the consumption of oxygen are read 

 off on manometer tubes. 12 



Limits of Availability of Above Methods. The adverse 

 criticism which Foa expresses for all the existing methods 

 except his own is certainly not correct in case of the mal- 

 achite-green method; and in the author's opinion it is ex- 

 tremely doubtful whether his method is practically any ad- 

 vance over the latter. The total oxidizing effect performed 

 by an extract or a tissue-pulp can be determined with ap- 

 proximate correctness by the methods mentioned and by 

 several other procedures 13 and compared. However, the 

 principal difficulty in the study of tissue peroxidases is not to 

 be found here. There are two great impediments in the 

 way, over which research has hitherto been stumbling. The 

 one is the impossibility to quantitatively extract the tissue 

 peroxidases (the same is true of other "endo enzymes ") 

 from the tissues ; the other is the blood in the tissues, 

 which, because blood may also act like a peroxidase and 

 because it can hardly be fully removed, makes all compara- 

 tive study of the peroxidase-content of tissues a matter of 

 uncertainty. That there are differences in this respect be- 

 tween the various tissues is shown by histochemical observa- 

 tion. If, for example, a cover-glass preparation of gonor- 

 rhoaal pus be treated with a peroxidase reagent, as benzidin- 

 monosulphite of soda, the leucocytic granules alone will 

 become colored at a certain stage of hydrogen peroxide con- 

 centration ; the myelocytes from the bone-marrow also are 

 easily stained, while the lymphocytes react only at a higher 



11 C. Foa (Mosso's Lab., Turin), Biochem. Zeitschr., 11, 382, 1908. 



12 H. H. Bunzel, U. S. Dept. Agricult., Bureau of Plant Industry, Bull. No. 

 238, Washington, 1912. 



18 Of. Literature: H. H. Bunzel, 1. c. 



