Enzymes 219 



Urease 



Sen^^^ described a method for the demonstration o£ urease 

 in the jack bean. The unfixed seeds are incubated with urea 

 and cobalt chloride in 60-80 per cent alcohol (urease is ac- 

 tive in an alcoholic medium ) . The precipitate of cobalt car- 

 bonate is demonstrated in the form of sulfide. 



The writer finds that the method does not work with ani- 

 mal tissues. 



APPENDIX 



Buffers for Use in Histochemistry 



The pH values in the tables which follow are only approximate but 

 are sufficiently accurate for histochemical purposes. 



0.2 M CITRATE BUFFER 



Solution A: 4.2 g. of citiic acid in 100 ml. of water. 

 Solution B: 5.9 g. of sodium citrate in 100 ml. of water. 

 Add a few crystals of camphor to both solutions. 



0.2 M ACETATE BUFFER 



Solution A: 1.2 ml. of acetic acid in 100 ml. of water. 

 Solution B: 2.7 g. of Na acetate (CHaCOONa • 3HoO) in 100 ml. 

 of water. 



Add a few crystals of camphor to both solutions. 



134. Sen, P. B.: Indian J. M. Research, 18:79, 1930. 



