VACCINES AND ANTITOXIC SERA 71 



this same bacillus must always be injected. Antibodies are not only 

 formed against bacteria, but against other organized material. If, 

 for instance, human blood serum is injected into a rabbit, there will 

 be formed antibodies against human serum in the rabbit's blood 

 serum, and if sheep's blood corpuscles are injected into a rabbit 

 there will be formed in the latter 's blood serum antibodies against 

 sheep's blood corpuscles, etc. 



Antigens. Any body, be it a bacterium, an animal, or a vegetable 

 cell or other organic product of any kind, that is injected into an 

 animal by the paraenteral 1 route and causes the formation of anti- 

 bodies is called an antigen (meaning to produce antibodies). 



Vaccines and Antitoxic Sera. The term vaccine (also vaccination) 

 is derived from the Latin word vacca (cow). It was first used for the 

 procedure of inoculating superficially the arm of a person with the 

 contents of a cowpox vesicle or the contents of the pustule from 

 another person. This method, as is well known, was and is used to 

 protect persons so vaccinated against smallpox. Today the term 

 vaccine is used in a general sense for any infecting living virus (bac- 

 terium, protozoan, or invisible infectious microorganisms, or their 

 toxins), either in full strength (virulency), in a very small does, or 

 in an attenuated form in a larger dose, for the purposes of producing 

 antibodies; that is, for the purpose of preventing or curing disease. 

 Some pathogenic microorganisms may even be killed by high 

 degrees of heat and still be effective as vaccines in the production 

 of antibodies. 



Preparation. Reference has been made to methods by which 

 pathogenic bacteria can be attenuated in order to be used in the 

 preparation of vaccines. These various methods are: 



1. Temperatures moderately higher than the optimum anthrax 

 vaccine. 



2. Temperatures which will kill the bacteria tuberculin, black-leg 

 vaccine, staphylococcus vaccine, streptococcus vaccine, pneumococcus 

 vaccine, colon bacillus vaccine, plague bacillus vaccine. 



3. The addition of antiseptics in small amounts carbolic acid, 

 for anthrax vaccine; iodine, for tetanus vaccine. 



4. Drying rabies virus. 



5. Digesting the bacterium cholera spirillum vaccine. 



6. Prolonged cultivation in artificial media fowl cholera vaccine. 

 Vaccines are, as seen above, generally prepared artificially outside 



of the animal body. Antitoxins, however, can only be prepared in 

 the body of an animal. The principle of the procedure is generally 

 as follows: Inject into an animal, say a horse, successively increas- 

 ing doses of, for example, a diphtheria toxin, and finally larger 

 amounts of cultures of virulent diphtheria bacilli themselves. These 



1 A paraenteral method is one of incorporation of a substance into an animal subcutaneously, 

 intraperitoneally, subdurally, intravenously, or by any other route than thegastro-intestinal 

 tract. 



