500 



PROTOPLASM 



by some other animal. The first method — that of active immuni- 

 zation — is quite successful in cases of smallpox and typhoid. 

 Smallpox may also confer immunity against other similar diseases 

 such as cowpox; or, what is of more importance medically, cow- 

 pox confers immunity against smallpox. Passive immunization 

 has had its greatest triumph in the case of diphtheria, for which 

 serum from an immunized horse is an almost certain cure. 

 Where acute diseases, for example, those of children, such as 

 measles, mumps, chickenpox, and infantile paralysis, do not 

 attack animals, the immune serum must be had from human 

 beings. Success has attended the prophylactic injection of 

 serum of convalescents from these diseases. 



Practical immunology has to do with the administration of a 

 substance that will combat a disease, that is to say, will lead to 

 the neutralization of the toxic substance in the patient. The 

 toxic substance may be living, or nonliving, viz., bacteria, a 

 virus, or an organic compound (not produced by bacteria). 

 There are many diseases of this last type, hay fever being one. 

 The agent causing the disease is a toxin, or antigen; the substance 

 produced and reacting with (counteracting) the antigen is the 

 a7ititoxin, or antibody. The production of an antibody, whether 

 in the natural course of living or through artificial injection of an 

 antigen into an animal, is known as immunization. An antigen 

 need not be poisonous ; more precisely defined, it is any agent that 

 will bring about the production of an antibody. The substance 

 administered may be a vaccine or an antitoxin (immune body) . A 

 vaccine is composed of the "attenuated," or killed, pathogenic 

 agent itself; while antitoxins are substances (possibly proteins) 

 produced by an animal which has previously had the disease in 

 question. The animal may have acquired the disease naturally 

 or, ordinarily in immunological practice, from vaccination 

 or the injection of the disease-producing agent. 



Special names have been given to certain immune substances, 

 or antibodies, and their corresponding inciting substances, or 

 antigens. Some of these are 



Antigen Antibody 



Enzyme Antienzyme 



Bacterial exotoxin Antitoxin 



\ Bacterial protein Agglutinin } 



} Vegetable and animal protein Precipitin ) 



Animal venom Antivenom 



