580 PATHOGENIC MICROORGANISMS 



they should be done. They take very little time and give the physician 

 a signal of possible danger. When such intravenous injections are 

 actually made in sensitive subjects, it seems advisable to dilute the 

 serum 50 per cent with sterile salt solution, in order to render slow 

 injection easier so that the injection of each cubic centimeter may 

 occupy at least one minute. 



Prophylactic Immunization in Diphtheria. There are two chief 

 methods of prophylaxis in diphtheria the first and older consists in inject- 

 ing 500 to 1000 units of antitoxin subcutaneously. This is carried out 

 on contacts with positive Schick reactions whenever speed of immuni- 

 zation is desired. It is simple and the principles underlying it are 

 obvious, but the immunization is short-lived and constitutes a sensiti- 

 zation of the subject with horse serum which naturally is undesirable 

 under modern conditions. 



There is another method of prophylactic immunization which is 

 rapidly growing in importance, and in this country is being at the present 

 time very actively worked upon by Park and his collaborators at the 

 New York Department of Health. This method consists in the active 

 immunization of individuals with overneutralized mixtures of toxin 

 and antitoxin. The possibility of developing this method is really 

 suggested in the original procedure adopted by the New York Depart- 

 ment of Health for the production of diphtheria antitoxin in horses, 

 namely, the partial neutralization of the first toxin injections by anti- 

 toxin. It was suggested some years ago by Theobald Smith that some 

 such method might be applicable for prophylactic immunization in 

 human beings, and subsequently the method was developed by the work 

 of Behring. 39 Behring made his first studies on animals, showing that 

 immunization in monkeys, guinea pigs, asses, etc., could be accom- 

 plished by such mixtures. His own first mixtures were so balanced 

 that the toxic action on guinea pigs was practically nil. Subsequently 

 Schreiber 40 and others studied the antitoxin production in human 

 beings. It was found that the results of immunization were noticeable 

 in about two to three weeks, and that 2 to 3 injections of properly bal- 

 anced mixtures would suffice to give a sufficient degree of immunity to 

 protect against ordinary spontaneous infection. Park and Zingher 41 

 originally recommended three injections at intervals of six to seven days, 



39 Behring, Deut. med. Woch., 39, 1913. 



40 Kclireiber. 



41 Park and Zingher, Jour. A. M. A., 5, 1915, 2216; Park and Zingher, Jour, 

 Amer. Pub, Health, 6, 1916, 431, 4 



