Effects of Bacterial Growth on the Environment 185 



former hemolysins are antigens and are liberated by bacteria, while 

 the latter hemolysins are antibodies produced by the host as a 

 result of antigenic (whole blood cell) stimulation. 



COAGULASE 



Part of the vital defense mechanism of the body is the depo- 

 sition of fibrin and the clotting of blood. Bacteria which have 

 gained entrance into the host animal may be kept localized by these 

 reactions. A substance called coagulase hastens the clotting of 

 blood plasma. Plasma is the cell-free liquid of the blood and 

 contains fibrin. Blood serum lacks fibrin and hence is incapable 

 of being clotted by coagulase. Staphylococci tend to remain local- 

 ized when they set up infections in the body, and the ability of 

 these bacteria to produce coagulase undoubtedly partially explains 

 why these infections remain localized, as in pimples, boils, car- 

 buncles, and the like. When the blood stream is invaded by these 

 bacteria, the formation of blood clots, called thrombi, within blood 

 vessels is a characteristic feature of such septicemias (infections 

 within the blood stream). The word bacteremia, strictly speak- 

 ing, means a transient invasion of the blood stream by bacteria. 

 This is a temporary condition, but in septicemia the organisms are 

 multiplying— a progressive type of blood poisoning. 



Rennet, the enzyme which causes sweet-curdling of milk, is 

 another example of a coagulase. After death, the stiffening of 

 muscles in man and in other animals, called rigor mortis, is ap- 

 parently caused by a coagulating enzyme which converts myosino- 

 gen of the muscle into firm myosin. 



FIBRINOLYSIN 

 Hemolytic streptococci belonging to Lancefield's Group A 

 (those pathogenic for man) produce a substance called fibrin- 

 OLYSiN which is capable of dissolving blood clots, or plasma clots. 

 Hence, infections with streptococci are less likely to remain local- 

 ized; they become generalized infections much more readily than 

 do the micrococci which liberate coagulase. Much of the invasive- 

 ness of streptococci can be explained on this basis. Fibrinolysin 



