96 THE ACTION OF ENZYMES 



albumin by neutralizing it with a few drops of very dilute hydro- 

 chloric acid ; a precipitate indicates alkali-albumin. 



(b) Filter off the precipitate and test the nitrate for peptone by 

 the biuret reaction. 



(c) Carefully neutralize the solutions in A and B, then filter 

 and examine the filtrates for peptones. 



Ex. 55. Pour 2 c.c. of milk into a test-tube and dilute with 

 about 10 c.c. of water; then add two or three drops of Benger's 

 Liquor pancreaticus. Immerse the tube in a water bath at 

 40 C. for half an hour. 



Note that the milk is first curdled ; the curd is soon digested 

 and dissolved more rapidly and completely than when pepsin is 

 used (compare Ex. 53). 



Test the yellowish liquid for peptones by the biuret test. 



7. Proteases or Proteolytic Enzymes of Bacteria. 



In 1887 Bitter found that the cholera bacillus when grown 

 in a liquid nutrient medium produced and set free in the 

 liquid an enzyme which was capable of digesting fibrin 

 and gelatine. Since that date a large number of kinds 

 have been found to secrete or form proteases which break 

 down gelatine and other proteins into simpler com- 

 pounds. In the ordinary cultivation of bacteria the 

 presence of these proteolytic enzymes is indicated by 

 the liquefaction of the solid gelatine media upon which 

 the organisms are grown. The gelatine is decomposed 

 into peptone, amino-acids, and other simpler substances 

 which dissolve in the water present in the jelly. Where 

 extracellular proteases are produced, that is, where they 

 are manufactured by the living cells and set free into 

 the surrounding medium, liquefaction proceeds at a rapid 

 rate. Common " liquefiers " are, Bs. subtilis, Bact. pro- 

 digiosum, Bact. vulgare, Bs. vulgatus, and Bact. fluorescens. 

 A number of species are known which only liquefy 



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