488 BACTERINS, SERUMS — VACCINES — ANTITOXINS 



caused by an extracellular toxin, such as is produced by Bad. diph- 

 therice and B. tetani and in which the animal or individual is immun- 

 ized either by the production of an antitoxin within the body due to 

 an attack of the disease or wherei the antitoxin is injected into the 

 body. 



Bacterial immunity is where amboceptors or immune bodies are 

 present having been produced in the body by the influence of the 

 infecting organisms or introduced from without. 



An active and passive immunity are also generally recognized. 

 An active immunity is produced when the specific antitoxin or im- 

 mune bodies are produced within the body itself. As for example, a 

 dog that recovers from distemper is not susceptible to that disease 

 because the tissues of its body have elaborated and thrown off specific 

 immune bodies toward this infection. Passive immunity is where 

 the individual received from without a sufficient quantity of anti- 

 toxin or amboceptors with which to neutralize the toxin or destroy the 

 invading bacteria. As for example, the horse which receives sub- 

 cutaneously an injection of tetanus antitoxin is rendered passively 

 immune to tetanus. As a rule active immunity is of much longer 

 duration than passive. 



Terms Defined. A somewhat vague and not altogether imiform 

 terminology is used in the description of the various biological 

 products employed in the prevention and cure of disease. Eor this 

 reason it is thought best to include a list of these terms in common 

 usage with their meaning as used in this chapter. 



Vaccines. This term comes from the Latin word "vacca," re- 

 lating to the cow, and in its original application was used by Jenner 

 to designate the prophylactic agent to immunize against smallpox, i.e., 

 the virus of cow pox or " vaccinia." This was a living, attenuated 

 virus. Following the discoveries of Pasteur, Wright and many 

 others, a large number of agents came into usage for immunilogical 

 or therapeutic purposes. These too were termed vaccines. In order 

 to avoid confusion it seems logical to limit the term vaccine to apply 

 only to those viruses which are in the living, attenuated form used to 

 produce an active immunity. 



Bacterin. This term sprang up in connection with products 

 used for the treatment of disease following the discoveries of Wright, 

 Douglas, Leishman and their colleagues. They are really bacterial 

 vaccines and are called such by many authorities. They consist of 

 dead bacteria and the products of their growth, suspended in sterile 

 physiological saline solution to which is usually added a little disin- 

 fectant, as carbolic acid or tricresol 0.1 — 0.5 per cent. The objection 

 to this term (bacterin) is that it implies an extract of bacteria, as does 

 tuberculin. This objection does not, however, seem to be well 

 founded. 



Antitoxin. This is the blood serum of an animal which has 



