876 IMMUNOLOGY 



Hope-Gill, 1938), especially in areas in which kala azar is absent. 

 In 1927 Henry described certain serological tests for the diagnosis 

 of malaria, based on the observation that the serums of malarial sub- 

 jects flocculate in solutions of metharsenate of iron ( f erroflocculation 

 test) and of melanin pigment (Henry's test, or the melanoflocculation 

 test). As a reagent for the Henry test, which was shown by later work 

 to be more sensitive than the ferroflocculation test, Henry (1934) used 

 the filtered supernatant from a suspension of finely ground choroid 

 tissue of ox eye in distilled water. This material after formalin had 

 been added and it had been kept on ice for at least several hours, is 

 added in proper proportions to the serum to be tested, and flocculation 

 is looked for after a half hour or more, preferably by means of the 

 photometer of Vernes, Bricq, and Yvonne. Many subsequent papers on 

 this test have been ably reviewed by Greig, Von Rooyen, and Hendry 

 (1934), Trensz (1936), Villain and Dupoux (1936), de Alda Calleja 

 (1936), Vaucel and Hoang-Tich-Try (1936), and Proske and Watson 

 (1939). The upshot of this work seems to indicate that the test may 

 serve as an adjunct to the search for malarial parasites in diagnosing 

 malaria, but that its use is restricted to laboratories equipped with a 

 photometer and to areas in which kala azar, certain types of leprosy, 

 and certain other diseases are not common. Since it has been shown to 

 be due to an increase of the euglobulin fraction, which flocculates upon 

 dilution with distilled water or weak salt solutions, Proske and Watson 

 (1939) have developed the protein-tyrosin reaction, which is a quanti- 

 tative chemical estimation of the euglobins of the serum. 



Immunological Reactions in Relation to Classification 



Various immunological reactions, since they are frequently species- 

 specific, have been used to check and extend other biological classifi- 

 cations. In other words, the more closely two species are related, the 

 stronger, in general, is the group reaction between them. This specificity 

 seems to depend on the basic structure of the antigens and haptenes, 

 which react specifically with immune serum in vitro. It also probably 

 depends upon the quantitative proportions of the various antigens con- 

 tained in a particular organism (see Wells, 1929). Immunological re- 

 actions can therefore be employed to compare chemical structure with 



