160 PUBLIC HEALTH BACTERIOLOGY 



the dry state by precipitation with alcohol. Such enzymes 

 are usually more thermostabile than when in solution. 

 Thus, most enzymes are readily destroyed in solution at 

 70 C, but dry enzymes may withstand 140 C. for 10 

 minutes. (As usual, moist heat is more effective than 

 dry heat.) 



This proteolytic (protein-splitting) or peptonizing power 

 varies for the different proteids, and is usually tried on 

 gelatin, blood fibrin, and casein of milk. Thus, Staphylo- 

 coccus pyogenes liquefies gelatin and blood-serum, and 

 clots milk, but does not dissolve the casein ; Streptococcus 

 pyogenes does not liquefy gelatin, nor blood serum, nor 

 casein ; B. coli communis is likewise negative to all three 

 tests ; some varieties of B. proteus are positive to all 

 three ; B. pyocyaneus is positive to the three ; Spirillum 

 cholerae liquefies gelatin and blood serum, but not casein ; 

 and so on. These tests are still very useful in dividing 

 the bacteria into groups, and so narrowing the field in the 

 difficult task of concluding, with moderate certainty, the 

 race of a particular germ. 



Note. Organisms which do not grow on gelatin or at air temperature cannot 

 be thus classified. 



HEMOLYSIS. 



Haemolysis will be treated of under immunity, but the 

 present reference is to the haemolytic action of certain 

 organisms when grown on blood-agar plates. (Blood agar 

 is made from defibrinated blood 1 part, and agar 2 parts.) 



