POSSIBILITIES OF SERUM THERAPY 233 



into an animal, the virulence is increased usually only for that animal 

 species, but may remain the same or even lowered for man. Many 

 authors, therefore, employ for the production of immune sera only virulent 

 strains of bacteria freshly isolated from a human being. 



In spite of all the above considerations, the fact still remains that most 

 immune sera excepting those of the cholera, typhoid, and paratyphoid 

 bacteria, show no bacteriolytic tendencies even under the most favorable 

 circumstances; but by means of their amboceptors they fix free comple- 

 ment and with the aid of bacteriotropins, stimulate phagocytosis. 



Whether complement fixation is at all to be considered as a protective 

 phenomenon, cannot with the evidence existing at present be definitely 

 decided. 



Conditions are much more favorable as far as the bacteriotropins are 

 concerned. Active phagocytosis is always an expression of good resistance. 

 It is not necessary for the leucocytes to digest the bacteria; it is 

 amply sufficient if a protective wall of these cells is formed (Ribbert, 

 Citron, Gruber) ; moreover they can neutralize the bacterial poisons. In 

 this connection it must always be borne in mind that phagocytosis by no 

 means necessitates the death of bacteria. 



Granting, however, that all the above requirements have been fulfilled 

 and a suitable serum has actually been produced, will such a serum always 

 be effective, or are there any other causes which may interfere with its 

 good results? In order to answer this, the infectious diseases must be 

 divided into acute and chronic. With the first class, success is quite 

 assured as long as it is possible to bring sufficient amounts of the active 

 serum substances into direct contact with the bacteria. In meningeal 

 infections, subdural injections may have to be adopted. It is difficult, 

 however, in cases of this nature to judge definitely whether the serum 

 therapy was really the effective agent, inasmuch as diseases like erysipelas, 

 meningitis, pneumonia, etc., are self limited, lasting for a period of time 

 and then subsiding of their own accord. 



With the chronic infections, on the other hand (especially tuberculosis), 

 serum therapy has a new difficulty to overcome. As a result of the long 

 course of the disease, it is naturally impossible by means of a single 

 injection to introduce sufficient curative bodies, as can be done in diph- 

 theria, for example. It is necessary, therefore, frequently to repeat the 

 injections. Under such conditions the human organism produces anti- 

 bodies against the foreign proteid (anaphylaxis) , perhaps even against the 

 curative substances in the serum (antiamboceptors) . In both instances 

 the desired effect of the serum is lost. A further impediment lies in 

 the possibility that bacteria remaining in a system for a long period 

 immunize themselves, and thus resist the action of the antibodies directed 

 against them. Such bacterial strains are known as " serum fast." 



