644 ACTIVE IMMUNIZATION 



The preparation of the vaccine is comparatively simple. The bacilli 

 are grown on agar for twenty-four hours, washed off with sterile normal 

 salt solution, standardized by counting the bacilli, and killed by heating 

 to 56 C. for one hour. As a matter of safety, 0.25 per cent, of tricresol 

 is then added (Russel). The details of the technic are given in Chapter 

 XIII. 



Metchnikoff has never fully accepted the belief in the value of heat- 

 killed vaccines, and at present is actively concerned with vaccines pre- 

 pared of living bacilli sensitized with their immune serum (sensitized 

 vaccines). Injection of these vaccines into chimpanzees is not folio wed 

 by any untoward effects, and apparently the bacilli so administered are 

 destroyed at once, as they have not been found in the blood, urine, and 

 feces. Metchnikoff and Besredka have immunized persons according 

 to these methods and report excellent results. Obviously, there is some 

 reluctance in using a vaccine of living bacilli until extended animal 

 experiments have proved that they are harmless and more efficient than 

 the vaccines of killed bacilli. 



As a general rule, the vaccine is prepared in two strengths: 500,000,- 

 000 bacteria per cubic centimeter for the first dose, and 1,000,000,000 for 

 the second and third doses. 



Method of Inoculation. The vaccine is best administered at about 

 4 o'clock in the afternoon, so that the reaction appears during the night 

 and is least likely to be disturbing. It is well to administer a cathartic 

 the day before the inoculation is made. Inoculations should not be 

 given during the menstrual period, as the general reaction is likely to be 

 somewhat severer at this time. 



The skin over the insertion of the deltoid muscle is touched with 

 tincture of iodin and the injection given subcutaneously. Intramuscular 

 injections should be avoided, as the reactions are more unpleasant and 

 accompanied by unnecessary pain on movement. In making deep 

 injections there is also danger of striking a nerve, a proceeding that may 

 be followed by disagreeable neuritis. 



After the injection has been given the iodin is wiped away with a 

 pledget of cotton and alcohol; no dressing is necessary. 



The syringe and needle should be sterile. Commercial firms have 

 placed the prophylactic on the market in syringes with sterilized needles, 

 accompanied with full instructions as to the technic of administration. 

 The vaccine should be well shaken before the injection is given. 



When a large number of injections are to be given at one time, a 

 single syringe may be used with a large number of sterile needles, a 



