DISEASE, INFECTION, AND RESISTANCE 303 



pollen, a marked inflammation and swelling at this point 

 ■will be noted. It will not have this effect if rubbed into the 

 skin of a normal individual. In a similar way an extract 

 from the hair or skin of the horse rubbed into the skin of a 

 person subject to horse asthma will cause a decided local 

 reaction. 



Occasionally individuals are found who are subject to 

 anaphylactic shock when injected with horse serum. Care 

 must be used, therefore, in injecting diphtheria antitoxin 

 and other antisera to make sure that the individual is not 

 markedly anaphylactic toward this protein. In some in- 

 stances the injection has been known to cause a temporary 

 illness and is not infrequently followed by the development 

 of a rash. 



Desensitization. — If a guinea pig be sensitized by the 

 injection of protein, and two weeks or more later a second 

 injection of the same protein be made in a dose too small to 

 cause fatal results, yet large enough to evoke some of the 

 symptoms of the anaphylactic shock, the animal will for a 

 time be temporarily desensitized. That is, after the ana- 

 phylactic shock has been evinced a third injection of the 

 same protein, unless much larger, will not produce the 

 anaphylactic symptoms. Use has been made of this prin- 

 ciple in desensitizing individuals sensitive to particular 

 proteins. 



Utilization of the Anaphylactic Shock in Disease Diag- 

 nosis. — When certain bacteria, particularly organisms 

 causing chronic infections such as glanders or tuberculosis, 

 gain access to the body they apparently act in the same 

 manner as a sensitizing dose of a protein. That is, as a 

 result of their growth in the body the individual animal 

 becomes highly sensitized to the organisms and the products 

 of their growth. This fact is made use of in the recognition 

 or diagnosis of such diseases. For example, a cow which has 

 been infected with tuberculosis becomes hypersensitive to 



