572 IMMUNOLOGY 



method is employed. Ramirez (1933) remarks that both Jadassohn 

 and Block popularized the patch test in Europe Avhile Sulzberger 

 has stimulated interest in the test in America. In conducting the 

 ' ' patch test ' ' one puts a small amount of the material to be tested 

 on an area of healthy skin, moistens it with water if necessary, and 

 covers it with a square of linen and then a square of rubber tissue. 

 These are held in place by a patch of adhesive tape. When posi- 

 tive reactions occur they do so, as a rule, within twenty-four to 

 forty-eight hours. Occasionally a reaction develops twenty-four 

 hours after the material is removed. They appear as an area of 

 redness associated with small vesicles where the material has been 

 in contact with the skin. 



g. Biological Test. — Since one may be skin positive and clin- 

 ically negative or skin negative and clinically sensitive to an 

 allergen, it is often necessary to ascertain by direct experiment 

 whether the patient is clinically sensitive to an allergen that is 

 under suspicion. This may be accomplished by ingestion of 

 specific foods after fasting where food allergy is under considera- 

 tion; by inducing attacks through exposure to specific inhalants 

 where the latter are under suspicion ; and l)y natural direct contact 

 in ascertaining the cause of contact dermatitis. 



h. Leucopenic Index. — Vaughan (1934) suggests that in food 

 allergy it is possible to show that the ingestion of the allergen to 

 which the patient is sensitive results in a drop in the leucocyte 

 count (leucopenia) within fifteen minutes and a return to normal 

 after ninety minutes. While Vaughan is apparently of the opinion 

 that the "leucopenic index," as it is called, will prove of value in 

 many cases of food allergy where other methods prove inadequate 

 in identifying the exciting agent, one should remember that this 

 test is not yet beyond the stage of experimental investigation. 



EosiNOPHiLES AND Allergy. — Aucr (1915) calls attention to the 

 development of an eosinophilia after delayed anaphylactic shock. 

 Davison (1934) lists eosinophilia as one oE the hematological find- 

 ings in allergy. It is generally recognized that eosinophilic cells 

 ak)ng with Charcot-Leyden crystals and Curschmanirs spirals are 

 quite characteristic sputum findings in bronchial asthma. Hansel 

 (1934, 1935) has> carried out an extensive study of the cytology 



