610 ANAPHYLAXIS IN RELATION TO INFECTION AND IMMUNITY 



areas may be observed. This test is not regarded as an allergic reac- 

 tion; a further description of it will be found in Chapter XXX, under 

 Diphtheria. 



Allergic reactions have also been observed, mostly in experimental 

 animals, in leprosy, sporotrichosis, in diseases due to hyphomycetes, and 

 in pregnancy. Further investigations will, no doubt, disclose reactions 

 of practical value in other diseases, such as rabies, scarlatina, measles, 

 etc., following the successful isolation and cultivation of their respective 

 causative microparasites. 



ALLERGIC REACTIONS AS A MEASURE OF IMMUNITY 

 Based upon the assumption that the antibodies (anaphylactins) 

 concerned in splitting their specific protein antigen at the local site of 

 application (as tuberculin, mallein, luetin, and typhoidin), with the libera- 

 tion or formation of the toxic material (anaphylatoxin) responsible for 

 the local reaction of infiltration, edema,, pain, and redness of the skin, 

 are the same as those which bring about the destruction of this protein 

 antigen in a living state as in the form of living microparasites, it is at 

 once apparent that these reactions are of value not only in the diagnosis 

 of various infections, but also as a measure of the defensive power or im- 

 munity of a person to a certain disease after recovery from this disease or 

 after active immunization by means of a vaccine. 



In other words, an allergic reaction may have a prognostic value. As 

 pointed out by Gay and Force, in typhoid immunization the continued 

 ability of a person to react positively to typhoidin may be accepted as an 

 indication of the presence of antibodies and of sufficient immunity 

 against typhoid fever; when, however, a person fails to react, this may be 

 regarded as an indication for further immunization. Likewise in cow- 

 pox vaccination an immediate or " immunity reaction," consisting in the 

 development of a small papule at the site of inoculation within twenty- 

 four to forty-eight hours after vaccination, indicates that the person 

 possesses the specific antibodies and does not "take" in the usual sense 

 of the term, because the virus or antigen has been acted upon at once by 

 the antibodies present. For this reason vaccinations should be inspected 

 within a few days after inoculation, as after five days this " immunity 

 reaction" disappears and the result may be interpreted as a failure to 

 vaccinate successfully, whereas, on the contrary, it may actually indicate 

 a state of immunity. 



