54 IMMUNE SERA 



Widal's. Hence, in acknowledgment of the labors 

 of the two authors most concerned in the discovery 

 and introduction of this reaction, we now speak of 

 it as the " Gruber-Widal reaction," whereas in the 

 beginning only the term " Widal reaction" was used. 



The manner in which the reaction proceeds in 

 microscopical preparations as well as when ma- 

 croscopically observed has been described above 

 (page 46). Nowadays the microscopic method is 

 given the preference in carrying out the diagnosis of 

 typhoid fever because in many cases it is distinct 

 when the macroscopic reaction fails ; and further 

 because the former yields distinct results within an 

 hour at the most, whereas in many cases twenty- 

 four hours are required for the macroscopic test. 



Pfaundler's Reaction (Thread Reaction). It 

 may be well at this point to call attention to a 

 peculiar reaction described by Pfaundler 1 in 1896. 

 This author showed that certain bacteria, though 

 they might not be agglutinated by a given serum, 

 would often, when they were grown therein, develop 

 in the form of long threads more or less interlaced. 

 This occurred only in the specific serum and was 

 absent in the normal serum. Most authorities 

 regard the thread reaction as a manifestation of 

 agglutinins. According to Metchnikoff this reaction 

 sometimes gives - more information concerning a 

 serum than does the ordinary agglutination test. 



1 Pfaundler, Centralblatt Bacteriologie, Vol. xix, 1896. 



