614 ACTIVE IMMUNIZATION 



Some confusion likewise exists as regards the terms serum and vaccine 

 therapy. Serum therapy is a process of passive immunization induced 

 for either protective or curative purposes by the injection of the blood- 

 serum of another animal that has been actively immunized by inocula- 

 tion with bacterial toxins or the bacteria themselves, as, for instance, 

 the injection of diphtheria or tetanus antitoxins. Vaccine or bacterin 

 therapy is a process of active immunization brought about by the injec- 

 tion of the bacteria or their products directly into a patient. Bacterial 

 vaccines that are simple emulsions of dead or attenuated bacteria 

 are not, therefore, serums, and the indiscriminate use of the two terms 

 is much to be regretted. 



Method of Preparing Vaccines. It may be stated that, in general, 

 the specific microorganism or virus used in a vaccine should be modified 

 as little as possible, or just sufficient to rob it of its disease-producing 

 power. For example, typhoid bacterial vaccine is prepared by suspend- 

 ing the bacilli in salt solution and exposing them to just enough heat 

 to modify them so that they can no longer multiply. The less modifica- 

 tion, the better the vaccine. If the exposure is too prolonged or the 

 temperature too high, the vaccinogenic power of the bacilli is destroyed, 

 and the suspension in salt solution is no more potent or of no greater 

 value than the salt solution itself. Therefore the nearer the vaccine 

 approaches the fully viable virus or microorganism, the more potent it 

 will be. The proper preparation of a vaccine, therefore, is the first 

 step to successful vaccine therapy. 



Vaccination, using the term in its broadest sense, may be performed 

 for prophylactic purposes and curative immunization in the following 

 ways : 



1. The living microorganism may be inoculated. This is the ideal 

 method, but for obvious reasons has not been generally used and is still 

 in the experimental stage. It is based upon experimental observations 

 made on the lower animals that an organism may be so introduced as 

 to render it incapable of producing disease, but may, however, stimulate 

 the production of specific protective antibodies. Most work on typhoid 

 fever is at present being done in the Pasteur Institute at Paris. Evidence 

 thus far indicates quite conclusively that the typhoid bacillus is unable 

 to produce typhoid fever unless it is introduced into the gastro-intestinal 

 tract, and the subcutaneous injection of living bacilli, modified only to a 

 slight extent by artificial cultivation, is not followed by ill effects and 

 produces a high grade of immunity. The principle is a good one, i. e., 

 in a vaccine the microorganism should be modified as little as possible. 



