QUESTIONS AND ANSWERS 341 



Serum Therapt 

 What is serum therapy? 



Serum therapy is a method of producing passive immunity. It 

 consists in the administration, for preventative or curative purposes, 

 of a hlood-serum containing antitoxin (antibodies) or some other 

 substance which is antagonistic to the bacterium or toxin which 

 causes the disease in question. 



Define immunity. What is meant by natural and acquired immunity? 



Immunity is a state in which an animal's body is resistant or 

 insusceptible to a certain disease. This state may be natural or 

 acquired. 



Natural immunity is that enjoyed by the animal from birth, and 

 not a result of any changes during its lifetime. If the immunity 

 is the result of changes during the animal's lifetime, it is spoken 

 of as an acquired immunity. 



Acquired immunity may be active, — ^that is, obtained by an in- 

 dividual by having suffered from an attack of a pathogenic micro- 

 organism and having overcome it; or it may be passive, — ^that is, a 

 result of the injection of the serum of an animal which has acquired 

 an active immunity against the organism in question. 



In what infectious diseases is immunization of value? 



In rabies, tetanus, black-quarter, anthrax, and hog cholera, im- 

 munization is unquestionably of great value. Considerable experi- 

 mental work has been done on immunization in the following dis- 

 eases: hemorrhagic septicaemia, influenza, dog distemper, Texas 

 fever, infectious abortion, glanders, tuberculosis, and foot-and-mouth 

 disease, but the results have been far from uniform and their value 

 is still subjudice. 



Discuss the antitoxin treatment. 



If gradually increasing doses of the toxins of a pathogenic micro- 

 organism are injected into an animal, the animal not only acquires 

 an immunity to the particular toxin, but its blood-serum will an- 

 tagonize or neutralize the latter if they are brought together. If 

 some of the serum of this immune animal is injected into an animal 

 which is suffering from the disease caused by this toxin, it will antag- 

 onize or render inert some or all of the toxin and thus aid in the 

 recovery of the sick animal. The substance contained in the immune 

 sera which combines with and neutralizes the toxin is called an 

 antitoxin. 



The treatment of an infectious disease with a specific antiserum 

 is called serum therapy. Diseases treated in this manner are 



