184 Microbes and You 



chemical reactions. Suffice it to say here that the metabohsm of 

 all cells would grind to a halt were it not for the action of these 

 organic catalysts we term enzymes. 



MISCELLANEOUS METABOLIC PRODUCTS 



HEMOLYSINS 



Hemolysins are agents which destroy red blood cells. They are 

 both filterable and thermolabile (destroyed bv heat), and when 

 injected into animals, hemolysins can stimulate the production of 

 antibodies called anti-hemolysins. 



When hemolysin-producing bacteria are grown on a suitable 

 culture medium containing whole blood, zones of clearing are dis- 

 tinguishable adjacent to colonies growing on such plates, and these 

 reactions are designated alpha hemolysis and beta hemolysis, 

 depending upon the nature of the change in the blood medium. 

 Alpha hemolysis (viridans type produced by pneumococci and 

 so-called green streps) is characterized by a greenish zone on a 

 blood agar plate. Examination of this discolored area under the 

 low power of the microscope will reveal that while a few intact red 

 corpuscles remain, most of the blood cells have disintegrated. Beta 

 hemolysis is characterized by a clear-cut colorless zone, and no 

 intact blood cells can be found in this clear area. Streptococci 

 associated with severe sore throats and pathogenic micrococci are 

 representative of organisms producing beta hemolytic reactions. 

 Any colonies failing to exhibit visible zones of hemolysis are called 

 GAMMA t\ pes of growth. There appears to be no strict correlation 

 between hemolysis and pathogenicity. 



Hemolysins are similar to bacterial exotoxins in that they are 

 given off in the surrounding medium and can be freed from the 

 cells by filtration. Bacterial hemolysins, however, should not be 

 confused with the type of immune reaction developed in animals 

 injected with the red blood cells of other species of animals. In- 

 jected foreign blood cells can stimulate the production of anti- 

 bodies (also called amboceptor or hemohjsins) which are capable 

 of dissolving the specific blood cells employed as antigen. The 



