378 Diagnostic Value of the Landau Test [April-July. 



Inasmuchas Landau suggested that each worker establish the 

 Optimum conditions for the test, and since he calls attention to the 

 labiHty of the active principle in the syphihtic serum, we made a 

 series of preHminary experiments, to develop a uniform technic for 

 all the cases of our series. From the very beginning it was quite 

 apparent that certain sera give a positive reaction, that others give 

 a negative reaction; and when examinations are duplicated, the 

 results of multiple examinations of the same sera invariably agree. 

 It is clear that certain sera possess a definite capacity to combine 

 with iodin and, in doing so, to form Compounds which do not re- 

 spond to the starch test for iodin. 



Our preliminary experiments have shown, however, that almost 

 all sera possess this property to a greater or less degree; and, if 

 left for a longer time, many negative sera, not having combined with 

 iodin at first, fix it ultimately. In his original article Landau sug- 

 gested that the test be allowed to stand for 5-15 hr. before reading. 

 Our preliminary experiments have shown, however, that this indefi- 

 nite technic may lead to very confusing results, for some sera give 

 very definite positive reactions even at the end of i hr. after the 

 addition of iodin mixture, some only after 3-5 hr., some only after 

 IG hr., and others only after 24 hr. Comparatively few sera fail to 

 combine with iodin by the end of 24 hr. In view of these facts we 

 permitted the mixtures to stand long enough to allow all the sera 

 giving a positive Wassermann reaction to combine with iodin and 

 found, in doing so, that 16 hr. was the best time limit. 



Another important question to decide was the uniform age of 

 the serum, as Landau in his publication warned against the use of 

 cid sera on account of their tendency to lose afiinity for iodin. 

 From our experiments in this connection it became apparent that 

 although some sera retain their property to fix iodin unchanged, for 

 even as long as 48 hr., other sera seem to undergo, on Standing, 

 certain changes that cause them to lose or to acquire the property to 

 fix iodin. We therefore adopted the uniform use of sera obtained 

 6 hr. after collection of the blood.^ 



Having thus eliminated the uncertain points in the technic of the 

 test, we proceeded to examine a series of 220 cases, using the follow- 



2 We also found that heating the sera for 30 min. at 56° C, did not change 

 their properties in reference to fixation of iodin. 



