PRACTICAL APPLICATIONS 359 



Immunity. The resistance against staphylococci appears to be 

 almost entirely dependent on phagocytic action. Ordinary 

 methods fail to demonstrate any bactericidal action, either in 

 normal or immune serum. Andrewes and Gordon, however, by 

 the use of special methods, have succeeded in showing that such 

 an action, though very slight, occurs even in the serum of normal 

 animals, and to a greater extent, though still but slight, when the 

 animal has been immunized. Perhaps the antibodies to the soluble 

 toxins mentioned above may have some protective action. 



The staphylococcus is very susceptible to phagocytic action, 

 and there is a general correlation between the opsonic index and 

 the stage of evolution of the lesion, as shown in Fig. 64. The 

 opsonic index is greatly raised in the serum of immunized animals, 

 and it would appear that injections of dead staphylococci have the 

 power of increasing both the thermolabile and thermostable 

 opsonin. The duration of the immunity is not definitely known, 

 but is certainly short. 



Diagnosis. This is made entirely by the demonstration of the 

 infective organism an easy task. In a few cases the opsonic 

 index may afford some help, being usually low during the acute 

 stage. 



Agglutinating sera can be prepared, but their action is not 

 powerful, and this reaction is useless in diagnosis. 



Treatment. Antistaphylococcic sera have been prepared, but 

 the results of its use are not encouraging, and the only valid 

 method is the use of vaccines. These should be prepared either 

 from virulent cultures derived from severe boils or carbuncles 

 or from the lesion it is desired to treat. In practice it is a good 

 plan to commence with a stock vaccine prepared from a virulent 

 culture, and to prepare an autochthonous vaccine for use if the 

 first does not succeed. In general opsonic control is not necessary, 

 and the doses may vary between 100 and 1,000 millions, repeated 

 every ten or fourteen days. 



Streptococcic Infections. 



The toxin of the Streptococcus pyogenes is still not definitely 

 known. We have already referred to the haemolysin which it 

 produces. There is some reason for believing that this substance 

 has some clinical action in acute infections, and that it is produced 

 to a greater extent by virulent than by non-virulent cultures, 



